Public Roads: A Journal of Highway Research, Vol. 13, No. 5

AA
Rhy
eey

Fee eo
ey eke

ids Afhs
714
‘ ede)
aN A eee

ee : eerie. * 7
! ahs ile iet ena ulp rane mene. sist ate st etelte
; \ ; f Ms ¢ Pewee 4. my + (ys oH - io
( : 4 Cdieh sl chah eo ; iA . Behe gk Punt
he abe bg) » , tyey eerie ¢ ¥ , reese oh gh ow *
One ee) UAC ae eee PAOON Me MeN oot 1k ot) Fee NN peat etal reek at 7 : { : 1 Th oe iy! ee ects ieee ekehe
ae AAR OF Dee ey LP Veo Pe ae CAA baat Mall A ARLE tye furl f fy M { i ; ‘1 ni lete ip
seh VO OOO DER bw 0 hay py #% ape is OC PASS ore ath ate, : ( A te PE : a ats el ne t
‘y PPPs es Pee Dee Re PR Rah . AM RAMA are ¢ rei : ; 403 ‘ ‘ ih , py oxy oe
Aa A AM Pe WAR a AML ATT tA tore BAR AE UCIT a, SiG ihg ebes ‘ Fy, ; oy y ert! eee
aaa ws 4 ie eh BREA Ie Chow ¥ APNE EEW EY Hy ey Shr beh bebe} ; a ¢ ‘i : ! * Lphehea ney pas gies y
7 a4 LAA A) WAT 8 Ey WP emp eA BF eae oe es iy renee. js 7 ns 4 “f ) : + y
VERO Leh ad eee oe bite) wee oe ba bay hopes eae Lay REA F , ‘ { ot hy eet ft raph f
Ache Daal ee OO Ree ee ae Ra om at AM Fak ee Oe MOE aA TREE ot: 4 wie r tS ‘s ite Ue
AAA At A EN Moris Mf oe ans ie Aen eee edhe) ie Wee Cr
oH PEAY HAY, s ’ sa ’ tow vo to ha
VPP OAT EGR ’ RPL AA hk nde Met ¥
va NK) CA te ee x ’ - .
‘

see bedeis peek Oe

CAA

‘ LAs

Wt dpi Soaoe
| ,

1 hea ey As
‘45

“ae AAD *
Peed Ads a,

t it ie
SDS OO FOE OF
LAA ARIA

eee Y Hr trie
ve ote ew

‘ pos
ache Pia wt seal ‘
* ¥}, rine HI9
LSA AAA,

wr
‘
iy

ACEP 89,39)
+349 9a 49 5
Lr eerie ks

Rs
ret ss x
pair tthenes
asaberse ts
Lape 8
ens * t

es

Sy aie aw
TAMA
Vite aw aye ag Mt

+
‘ a) os
yes tet rer Ai a Oe 4
LACT A TORIE IESE IE kere Seat
OSPR ee ed eee
PALM MI CIEE Ce
Meh e? ie KAA) Rahs
saad Oke Hae Aire rete
LH AGA CRE We Vevey) Hae e aad we
they Pa ata ately pate nae

it

+ do
VES OTe dg9 Veo eae , titer
SUC T AA eb oy Rnd bg kes ae
RASA AH \ vin) Apa oe ey
’

ae AA ay
Dae

Ee
oe
=

a .
fe

t- .
et?

‘ rahe aay

oa
aM
i Fe ee y sevie Crs
4 ie ere ie
. t thts BN ey stoiete i x GC
p>. Hat 4 pw ILI i ‘|
ith Kv Hen

Tea vara yet
dine RG) SAG

i ne
WA ra varity)

UL ASS a Ten
H Lee oe
Whiciri dich Ae AcE, nmi! :
DAAC R ISON MSN CSE aR Ie tn

i
1 +e
SA LRA HO mee
+> Mt 4 vite es Ved aan, Ai b ns ky 0 be rib
; WSS ONS RUM Re Meat teamenyeoir ait
, ste r , Sy) ie ne 7 RSA RANGA sees br monte it % i one
bad CWE Ret ere RRR AMC ie ne Wat he Riskslel braplek slit ed
ae irs ASU A PUMICE ST is Ic ta CAC RAL A MARR. ree wht ee aa erp hens
ee wah aS br Aen MRL Ie he HE DVO VOTED a) hee , it tehet
einen a cvletcees AUIS titala tet ene Ae WA AA
PORORA KS aie aati AA aN ON Rat SNe a8 ae yey
Ada J RRA A ICE, PUA Re oy 4 href eh
Way Nt) DEP ORICR SCIEN ein COCR IER Mure eT
hie SOUR RACK Ui OU AN ARIR CMe MORSE WCNC CAL
¥ * bok Hs vs Cea a) AN LAPUA 1 he
a VVeer Ly wae tk COAU N
i) iin * A Ny Wee, siete tat
MARCA OLVUA A SOW AA ACA
* veh AAS LAAN: tae Ait aA?
ahaa MEN totite MEN eh

Diet Ate Mt td tae et : TE as a A PRE
Pat yi FE EMPK TG TA HNN Ne y
DA ALt Ae Ae Ae Oe Via Aes
SUV O PPR eT ee
A CO ee
PAW OT

iy
Nata

a)

* Way eH dea A SOO Cet
aw nit be Mead Me aca ht il et
¥ hi hari ‘ata Ry iat Ht x 4, bt eh ‘ yh Ks * ai Tvalatwaten

SAYER ES CVA GTA: VR a
ey ita tat nti y ay, CNAs int ay LAA yi he
SENN nL rhs UCU AA MA itaaty! RA, ‘ Arata ORAKN? i
Ainareasitat stat Sait mn scat A Ny tats RT HOIGRIENUONC HRI Pes ekyhe tal HANNA at amie
Who ay 4 Vn erry eA An WAVES YY anyrd te ep aa tyra ma ts i i
Away Pei ty Pegi WAAL Wa oP ea ALA br
DCA Ne ELM ANG pte ALTA
a

LA \ r NM iJ , Pan x
' Dae VRE SEN A Da ye Ek cae oe
CUM UN Ru NORA ay
Fe WAS Eh) SAW ANG feats a '
Pee Fe Ya a POPE PATS thle th 0 kd SAP ON Ok ae th a Ad
LARC SUCPE RCS Mi Ne Ve We te We EPR EV GREE Pa Dh be bata tke
BAAN Te Me Se hk Ce ete he MD LAA UOC as
VAAL OM Eee ho SW Je He i ba SURAT AY Ob hyde
ya tana yt Sth Poi Bec EN Aa yay 5) els ‘y
MMe ieiti til hk Die) Mae ates tetany WARNS ea whe
awh eR ERO int oD HM Pratik aM] aN eaten
OUR RAC Meet tat ans MAT CALANL A HC) Tarnt dd p vacate hahah tA *

Tet Loy "
‘ AO Vergy ys! ha Mv awl eek as
ral sytata arnt HN At) ANN Bis 4 ve LAER MEAL Tbe Lk Toe We ct

LOR hed!
en aty

era) \ VES EPR EH UE gb ‘
Aa Paradies ik BL Te ee Behe Be A Vad sees aad OF 4 Leer ey ‘7 ( pay
Uy ER Lavan pty : Wy Hee vty SHAS ey a uh shh : nes ate
AAA UNS Bs Me Te SL Ye ih Ms Re he Sota SUA A ENG Racy hea a yay he is yee ah
“ef RAE Me tf Ware RAL MEE OG ae Oe Wee Te ROP EVO Ae ® abc ete Pe bets
iota cater a te a Tati ht ne ARP, Ha eee cbt oS AAP WA Rn i tr ty
pea wth 3 ate pha taa tha vey AS eho Arb Vy yy ty ash D0} e ea hew wee
a ke v AAA AN ALS Pettit SAA AS Oe at icine ry ws
Vos NAO RSS aw AR) GAA VN 4 AAT * f sick’ Cire rh
4 i *4 Pewee Wk alat
Viera Pe ety ad ey by EW A eek al el Wr recent ie
Pata tate’) aaa Ne W's iha's that eae A URLIRC REE ibd Amaeetls rere van!
ay x) ‘ Pam) ara teks
DOOM RTH WAC OL SA OMG Cena ie its serrate rSinenie oe
PAULA Hag yg yy Vee de ba ay ¥ an Bi iy
y SUR IORK AEWA LRA AC CROCCO MORN Hehe ah Puacisciate Vey pian
Ra N AH ata ges eta a tals ta) OG Me abe eh hw al OC Wiens . at J ae
WIHAA YA TEA yh yh Nes DALE CMe te i | CAUCE RL eee Nebr 33 eiesarri arabs
iA AOL RARGR TEI H bebe eA ataconi pha ats ati tabtaes hee Braratany Wg a < Mitts Age
wey *) Vr LUVENN YE ay a ae iC SANA ATO CLA WG LM LIK ea ast OMe ie kyr ues Li ee te Bo
Ve abe PAOLO EOCaY wor ire ‘ Ly APIS NATAL ICI A A A Meeks inl ic a
Neha FV a ” PER, NOS ANA OA RA SOR TO Aa ted Bo SRL ht pty
WONG A Ae yy 628 WAV Lepr als Aa em neh ts v4 S94 ore HE Te Hy ee at A tt AIO ON ASAP ‘he rare he 9 1 0a
eS ean ee hae Wate La tit AKALAA EO CU AAA! Miia seats Natit ital! NSE UE a pate ere fabs Chad -t
Veteed MG Ah yy . ee Vea \ 47 J i bd} + a ete Z
AA ARON a RE OUNCESA RHR RIOR RR WAS AAO DACA Brattain OAR AA EAE tt tte ba bets ites:
' ah A pt ’
OLR Se AREY Seventeen te
‘ FUiteatetat ‘teary Sran ea eaerea pattie
yee A Was lva Msisiesrer? 7
AAS De ale ant?
1 A 4 PA ey a
WA AAS whe Upwear
ees wan AYR eee ed aeae
ARS Hee +

; y WS ARR
, CHT TRE ERLE ENS AAO RS LA HS
SAT AEES HAA YR TRE Ae ow »
SVVUTN AR Sk ee SUAS Oy a a ary

> WAC A MD Aw pth DRA RAR ant
PUNRPAND He LOD Hale

: bike
VAVA we WR We ica tt
SERV ARMY Dy aay at
va ys ASA AT We wate ee 1%

¥ Rea ye he
OGY RO EA oak. BL AAA AN rik meets tt
ONAN D4 ey ‘i PAL AA AOL CRON Sarna ck nt
9) rs SEAM Be Ae Ae TOVREA A PANS Ba eats
LOA ne ee Loe eee SAUL RAL tn tek +
TAS SOR ee eA PAA, a HA ASR OUR Lee COC) ah uA
THe Bae LAA eee ey LUO bea ee a Aly 4
rls Lae ¥ (Vie %¥, a
‘ Ay >
Whee oe a
BAAN ‘ "abi gsireate Cat
Vate ey \ PRESS Vee ‘ Nn vi
OVE LETY Viarhe agg ’ ‘ Levees Us dh ee Oeerat MOTO OLOLY He
Pe A the * ‘y Lua tA "i a svelte che A A A}
’ Co . phy >
sehen Sea te Ce ox Lhe ‘eae
NWN SNS ae a SSR CELT te none
Le te oY e's ae
vee uke
Laha8
we Vee ee
Vk ae

, ms
tVAWA RAW Oe Rad

ee
eee eh eee & ~*~ Haetie es
Seen puri reuieret
Pecan an Cae Sete ut peat

i he ee Oe LAA
A i i ; eas cages tors ve nea eran ater sighed
% ‘ , ; ! J ar ie hk tee arth 3 a . it astra kcerackpanh, ae
LAM oe te a aS 2 * PRS 2a 4) ‘S * . barby ty F * y ry
VEVVARARW DED RS aA Why veh ay s TOO Area nea re Ld sage: . hy 4 Ls SOIR
LARA Se eS AV wHR LAA LAS Ge OS Cas , aeke keh AAM ' by . ‘ ee wea arta
‘yee VAR Uvey oad WAPOA PLAGE Se Wey hve et i eh oe abe ery oui
x VINO a hy ay Lene 4 fAAL TEN Sr ta he & * . |
| LE OM NVA SENN OO ONS AY RAW Ee AAI: “We Ae | AAA
ve V\POeA eA
AON eee
‘ VER RN DAW Dae
** J ay ‘

. a4 4 . \ Wa ee Oe
PLT Se LENA EET ee ae

A , \
vanear ‘ WALA ALA toe Ke Sy Wy an a
VO AE tee Ah Oem Be gage, .

ee en * 4

iT.

=
ers
By
>

a

=

2
=
Se
=
Bie
#
aay
—-
f
¢.
“ice

ve
*
a
Se
<F
=
er
ele
3
aiteets
27
oe;
Ee
+
fg,

7 eee aN bis ire
3 a 1o 4euee Avs TASS aS : by ay ahs reriy erty tat eh he
so ahe 4 wR ¢ ANA TAS Hite yw Oe WAST RRAA SURAT SALT Ce ht an nt AGATA ch ere ee morees ma
eRe LU VAN OT De bad ay 5 NOGA A AVANT AREA AM AIAN CCEA NL K ATO Cr bos Nhe Fee Be we Oi te tare re tar me bh
hah ee PO eC ; 4) ee Wo etre nt ‘ P¥Prd ee AAA Ager tte: re ee oe oe ee bobel i *
aeurhe TVVeD eee SWAT UM ANSE Wash NA ate sat NM it CaF ie Lary Ath ty bei aA zr
Seer a eee SENEGAL On RIE RICHER RICH ILRI SEIN DAR, 8 ee LAA AL ey te Ae ar
aa 1 ae we We oe Le a4 ean * 4 LA MURA © aor ie > .
»* a ak " " .
~

- id

a 2 a @ a
4 -$e a ~~, ;
=a ee at ame
Teh. 4, wee
a Ma

ipa

> -
—) J hed

od

.
¢@
®
aa ot

»

UBLIC ROADS

inl

D ln. “al lh, ‘ly. “all A(t, vail, :

A JOURNAL OF HIGHWAY RESEARCH _

Ve =

(@))| UNITED STATES DEPARTMENT OF AGRICULTURE

ess i BUREAU OF PUBLIC ROADS
inc: err =

aCe) Lee LS ee IN, GD Pr V SMT ne RS re ee

ON THE MOUNT VERNON MEMORIAL HIGHWAY

For sale by the Superintendent of Documents, Washington, D. C. - - - - - - - - - - - - See page 2 of cover for prices

PUBLIC ROADS2.2722

UNITEDSSTATESSDEPAK IMENT OGSAGRI GU ERURE
BUREAUMOL GP UB Gah OADS

G. P. St. CLAIR, Editor
Volume 13, No. 5 July, 1932

The reports of research published in this magazine are necessarily qualified by the conditions of the tests from which the data are
obtained. Whenever it is deemed possible to do so, generalizations are drawn from the results of the tests; and, unless this is done,
the conclusions formulated must be considered as specifically pertinent only to the described conditions.

In This Issue

Page

The Design of Street and Highway Intersections

THE BUREAU OF PUBLIC ROADS - = =) WillardsBuilding? Washington ae:

REGIONAL HEADQUARTERS =~ = - - = = =. -wMark Sheldon Building, SanFrancisco, Calif:
Vv
DIS ER TGTO isle rss
DISTRICT No. 1. Oregon, Washington, and Montana. DISTRICT No. 7. Illinois, Indiana, Kentucky, and Michigan.
Post Office Building, P. O. Box 3900, Portland, Oreg. South Chicago Post Office Building, Chicago, III,
DISTRICT No. Dy California, Arizona Nevada, and Hawaii. DISTRICT No. 8. Alabama, Georgia, Florida Mississippi, South Carolina,
Mark Sheldon Building, 461 Market St., San Francisco, Calif. and Tennessee. 28.
Shepherd Building, P. O. Box J, Montgomery, Ala.
DISTRICT No. 3. Colorado, New Mexico, and Wyoming. DISTRICT No. 9. Connecticut, Maine, Massachusetts, New Hampshire, New
237 Custom House, Nineteenth and Stout Sts., Denver, Colo. Jersey, New York, Rhode Island, and Vermont.

DISTRICT No. 4. Minnesota, North Dakota, South Dakota, and Wisconsin. Hedera) Building lrcy ae

210 Hamm Buildineise Pauls Minn DISTRICT No. 10. Delaware, Maryland, North Carolina, Ohio, Pennsylvania,
Virginia, and West Virginia.
DISTRICT No. 5. Iowa, Kansas, Missouri, and Nebraska. Willard Building, Washington, D. C.

Eighth Floor, Saunders-Kennedy Building, Omaha, Nebr. DISTRICT No. 11. Alaska.
Room 419, Federal and Territorial Building, Juneau, Alaska.

DISTRICT No. 6. Arkansas, Louisiana, Oklahoma, and Texas. DISTRIGLINe a 2nldahoand Urine
1912 Fort Worth National Bank Building, Fort Worth, Tex. 403 Fred J. Kiesel Building, Ogden, Utah.

Owing to the necessarily limited edition of this publication it will be impossible to distribute it free to any persons or institutions
other than State and county officials actually engaged in planning or constructing public highways, instructors in highway engi-
neering, and periodicals upon an exchange basis. Others desiring to obtain Pustic Roaps can do so by sending $1 per year
(foreign subscription $1.50) to the Superintendent of Documents, United States Government Printing Office, Washington, D. C.

CERTIFICATE: By direction of the Secretary of Agriculture, the matter contained herein is published as administrative information
and is required for the proper transaction of the public business. ‘

THE DESIGN OF STREET AND HIGHWAY
INTERSECTIONS

By L. S. TUTTLE and E. H. HOLMES, Assistant Highway Economists, United States Bureau of Public Roads *

WO general methods of solving the problems and

difficulties created by the increase in volume and

speed of traffic have been developed. One method
of control regulates traffic movement by such artificial
means as driving rules, city ordinances, traffic officers,
or signal devices, while the other seeks to minimize the
necessity of artificial restrictive measures through the
physical design of streets and highways for the free
flow of traffic.

This paper deals with two classes of intersections,
those where traffic volume necessitates regulation and
those where faulty design requires it. It is proposed to
show how in certain instances intersections may be
developed which will obviate all control devices and
rely solely upon the physical construction of the various
details to induce drivers to take the proper course
voluntarily, to give preference to the major traffic
without too severely penalizing the minor traffic, and,
when some control device is absolutely necessary, to
facilitate its operation by the proper physical design.

INCREASED EFFICIENCY FOR EXISTING INTERSECTIONS THROUGH
MINOR CHANGES IN PHYSICAL LAYOUT

Curb radii.—A detail warranting most careful con-
sideration in intersection design is the radius of the
curves rounding off the curbs of the intersecting streets.
Cutting back the curbs at existing intersections to
facilitate the right turn movement is a simple and
effective device for increasing intersection efficiency,
particularly where the percentage of right turns is
large.

A proper curb radius is one which can be followed by
the vehicle having the largest normal inside turning
radius. The largest radius which will be required for
any but an exceptional passenger car is under 25 feet,
but various types of trucks and busses have larger
inside turning radii. It should not be necessary to
provide for an occasional vehicle having a 40-foot
turning radius, but it is absolutely necessary for efficient
intersection operation that the radius be sufficient to
allow the normal vehicle to follow the curb in turning
and, for this reason, a curb radius of 30 feet is recom-
mended as a minimum for highway intersections and is
incorporated in all the designs presented.

For street intersections this rule applies only when the
vehicle making the turn approaches in the outside lane
of the roadway. Such would not be the case if parking
were permitted along the intersecting streets and,
while a 30-foot radius would be entirely satisfactory
from the traflic viewpoint in this case, it may unneces-
sarily restrict sidewalk area. In this instance the
proper turning radius depends not only on the vehicular
requirements, but also on the sidewalk width and
parking restrictions. If parking is restricted for a
distance back of the intersection to allow another lane
of traffic to collect while waiting for a signal, then the
radius should be the same as for an open highway
intersection, but in the case of the intersection of minor
streets where there is no control and consequently no
accumulated stoppage, parking should not be restricted
so severely and so a design for curb rounding as shown
in Figure 1 should be developed.

125304—32

The above discussion concerns only the minimum
turning radius of vehicles and results in a turn which
restricts the speed to approximately 12 miles per hour.
Obviously, in the case of an outlying intersection where
land is available, it would be desirable to increase this
turning radius to some figure which would permit higher
speeds. This step becomes important at heavily trav-
eled intersections. If the speed which would be main-
tained provided there were no turning traffic is 20 miles
per hour and the radius of the curb of the intersection
is such that only 12 miles per hour can be maintained
in the turning, turning traffic will unnecessarily retard
through traffic, materially reducing the capacity of the
intersection. Therefore, it is advisable to design the
turning radius to accommodate the same speed which
would be maintained by traffic moving straight through
the intersection, except where a heavy pedestrian move-
ment will control the turning speed.

7 PARKING LANE

ROUNDED FOR PROPER TURN-
ING RADIUS, SERIOUSLY DE-
CREASES SIDEWALK WIDTH

SHORT RADIUS CURB; EFFECTIVE
WHERE PARKING IS PERMITTED.

Figure 1.—DrEsiGgn or SHort-Rapius CurB

The speed which will be maintained around a curve
will vary with the individual driver, but usually will
not exceed that at which passengers begin to feel dis-
comfort. This discomfort results from the effort to
maintain an erect position in overcoming the centrifugal
force resulting from the deflection from a straight course.

In order to determine the uncomfortable rate of de-
flection a series of test runs were made around curves of
various radii in a coupé and also in a sedan, both in the
lower price range. When it became necessary for the
occupants to exert a distinct effort to remain erect, a
speedometer reading was taken. While this method
was rough, the observed speeds plotted against the radii
gave a remarkably smooth curve, the two cars showing
close agreement. Theorectically the curve should be
a parabola since the centrifugal force varies as the
square of the speed. A parabola was accordingly fitted
to the data by the method of least squares, resulting in
the following formula:

R=0.22 V?
where F is the radius of curvature in feet and V is the
speed in miles per hour. The comfortable rate of de-
flection as computed from this formula is 9.7 feet per
second per second, and the tendency to skid is 0.3 the
weight of the vehicle, which would be > generally accepted

> Digested tenn a thesis ripened for the masters’ daarea at ated Rugsél
Erskine Bureau for Street Traffic Research, Harvard University.

73

74 PUBLIC
as a safe condition. Computed comfortable speeds for
various radii of curvature are given in Table 1.

It is obvious that higher speeds may be maintained
with safety, and, if the curve is followed for only a
short distance, without particular discomfort.

TABLE 1.—Comfortable driving speeds for various radii of curvature

Radius Speed Radius Speed Radius Speed
Miles per Miles per Miles per
Feet hour Feet hour Feet hour
20 10 200 30 600 52
30 12 250 34 700 56
50 15 300 37 800 60
100 21 400 43
150 26 500 48

Splayed intersections.—Closely related to the improve-
ment of curb radii is the practice of splaying or widen-
ing the roadways at the intersection. This device has
been used in many places. Successful examples are
found in Cook County, Ill. and in Reno County, Kans.
The Illinois design provides an additional lane on either
side of the pavement for a distance of 300 feet from the
intersection. ‘The Kansas design eliminates the inter-
section altogether for turning traffic by providing turn-
ing roads of 200 foot radius. Such treatment reduces
congestion by removing much or all of the turning
movement from the intersection area. The design of
an intersection of this type depends upon the locality,
the available right of way, the volume and character
of traffic, and the percentage of turning movement.
A suggested design is shown in Figure 2.

oF Two 30-rootT Roapways
FOR TURNING

Figure 2,—INTERSECTION
SPLAYED

At,heavily traveled intersections where control
methods result in considerable stoppage, splaying may
prove advantageous to through traffic as well as to
turning traffic, by permitting the accumulation of
vehicles in a greater number of lanes, with a resultant
shortening of the waiting lines. Before splaying an
intersection for this purpose, care must be taken that
the greater number of lanes may be accommodated
beyond the intersection to such a point that the
vehicles may resume their travel in the normal number
offlanes. Each additional lane of width increases the

ROADS Vol. 13, No. 5
pedestrian hazard, and necessitates a longer clearance
period in the control device.

Islands—To facilitate movement and to prevent
confusion, islands may be installed within the inter-
section or in the entering streets. This is especially
helpful when splaying or wide streets result in an
intersection of extensive area.

Medial strips are useful where it is desirable to sep-
arate opposing traffic movements and at the intersec-
tion of wide routes where proper alignment on either
side of the cross streets is difficult. The width should
be at least 4 feet and should be varied to such an
extent that the area remaining on either side can be
divided into 10-foot traffic lanes, with the possibility
of one 7 or 8 foot parking lane. The construction may
be concrete or a curb-inclosed grassed or planted area.
In any case, the curb height should be from 8 to 10
inches and the end confronting traffic amply protected
at night by a flashing or reflecting beacon.

Directional islands are normally located in the throats
of the streets composing the intersection and their size
and shape must be very carefully considered in order
that they will assist rather than hinder the flow of traffic
through the intersection. They are normally placed in
a dead area and are shaped according to the desired
flow of traffic. The islands should extend into the
throats of the entering streets for such a distance that
there can be no mistake as to the route to be followed
and, in case the islands are to be used for pedestrian
safety zones, they must extend to a point beyond the
crosswalk and be amply flood-lighted.

The natural tendency for a driver is to continue in a
straight line unless compelled to change his route
because of external conditions. Therefore, it is im-
perative that these islands, intended to align traffic
properly, be so designed that the obvious route for a
driver to follow as he passes the island is the route which
will bring about the most effective operation of the
intersection.

Directional islands may often be located nearer the
center of the intersection to delimit a neutral area which
otherwise would be a point of conflict for several lanes
of traffic. The sides of islands of this sort which ve-
hicles are expected to follow in turning must have a
radius which fulfills the requirements previously stated
under curb radi.

Many times directional islands are located at the
center of the intersection to serve merely as a point
about which traffic turning left must proceed. In this
case, 1t is not necessary to have a minimum radius as
specified above, for the vehicle does not follow the
island for any appreciable distance. The island here
merely serves to indicate to the driver the route which
will least interfere with the opposing traffic. Its loca-
tion must be such that any vehicle turning about it,
presumably to the left, will be able to do so at a con-
venient turning radius and will not be required to
swing out either before or after passing it with conse-
quent fouling of other lines of traffic. It will be noted
that the ordinary flashing beacons so often seen at the
center of intersections fall under this classification and
their location should be determined in the above
manner. Applications of this theory are shown in the
designs which accompany this article.

ROTARY TRAFFIC

Rotary traffic is here defined as the movement of
vehicles around a traffic circle or square in one direction
only. Such traffic circles and squares are usually
formed by the convergence of several streets. Where

July, 1932

the rotary system is in operation, vehicles are required
to execute a right turn upon entering the circle, pro-
ceed around the circle to the right, interweavi ng with
the traffic already upon the cir cular roadway and leave
at the desired exit by means of a right turn. The
circle should be so designed that no vehicle can pass
directly through the intersection. In effect this plan
creates a circular l-way street which can be entered
ot left only by means of a right turn, no left turns being
permitted. The rotary traffic plan intends a non-stop
flow of traffic although in special cases it has been
found necessary to control traffic by officers or lights
for the convenience of pedestrians.

The rotary movement of traffic is graphically pic-
tured in Figure 3, a typical design for the right-angled
intersection of two 4-lane streets or highways, the paths
of the vehicles being indicated by means of arrows.
It will be observed that there are four points of conflict,
one such point arising about halfway between any two
entering streets. The basic theory of the system pre-
supposes that actual conflict will be reduced to a mini-
mum since entering vehicles are forced by the form of
the intersection to interweave with the traffic already
upon the circular roadway by proceeding in the same
direction. The two traffic streams converge and mingle
and there is no direct conflict of direction. The flatter
the angle of convergence the easier and more efficient
is the interweaving process. This angle of convergence
bears an inverse relationship to the diameter of the
central island, the angle decreasing as the diameter is
increased. However, there are factors which limit the
size of the central island, such as the amount of land
available and the greater inconvenience to the traffic as
the length of travel about the circle is increased.

The central island.—The function of the central island
is to produce a true rotary movement. For best re-
sults, conflicting streams of traffic should converge at an
oblique angle and there should be sufficient length of
roadway between entering streets for a complete and
easy interweaving of vehicles. The shape and size of
the central island or obstruction around which traffic is
required to pass, therefore, has a marked influence on
the efficiency with which traffic is handled. Ordinarily
the circular form of central island is desirable as best
fulfilling the above conditions, but for intersections of
radical design special forms of central island will be
required. At a right-angled intersection where the
traffic is much heavier on one street than on the other
it is usually desirable to give traffic on the major road
preference by using an elliptical form of central island,
the long axis of the ellipse coinciding with the axis of
the major route. By this method the traffic on the
major route is given the advantage of easy curves at
the intersection and will be able to pass through with
greater speed and less delay than traffic crossing the
major route. Cross traffic will be forced to slow down
considerably and will filter through the main traffic or
turn into the main traffic stream when opportunity
offers with a minimum of delay to the major traffic.

The size of the central island is a function of the con-
venient turning radius of vehicles and the length be-
tween the entering streets required for the interweaving
of vehicles. Where traffic volume is large, this distance
should be at least 100 feet for efficient operation al-
though satisfactory results have been obtained where
the interweaving distance is considerably less. It has
been observed, however, that where less than 100 feet
is provided, the speed of movement is considerably
reduced as the traffic increases in volume.

PUBLIC ROADS to

The size of the central island from the point of view
of the speed which may be maintained through the circle
may be determined from Table 1. As mentioned be-
fore, this table is conservative and the speeds will vary
ereatly with the individual driver’s idea as to what
constitutes a comfortable turning speed; but it does
serve as an indication of the possibilities of a design of
this sort.

The radius of the central island is not the only factor
which controls the speed of vehicles through the rotary
intersection. It would appear from Table 1 that a
central island with a radius of 400 feet would permit
vehicles to pass through at a speed of approximately 40
miles per hour. Such would not be the case in prac-
tice. Vehicles would necessarily be retarded by the
interweaving of conflicting streams of traffic. Speed
studies on several rotary intersections indicate that
average speed of vehicles in passing through the inter-
section is between 15 and 20 miles per hour.

Ky
Wf

FLASHING BEACON _—-+-—”
DIRECTION SIGN

ag eee eer

21-27" L BRAKING DISTANCE
ace FOR LAWFUL SPEED

* CAUTION SIGN

Figure 3.—RECOMMENDED DB&SIGN FOR RoTary INTERSEC-
TION WITH CENTRAL ISLAND OF MINIMUM DIAMETER

The traffic studies at Lee Circle, New Orleans, show
that during the maximum hour 2,543 vehicles passed
through the circle and that the average speed during
that time was between 16 and 19 miles per hour.
Several observations at the rotary traffic intersection
of Old Colony Avenue and Columbia Road, Boston,
indicate that the average speed through this circle is
between 15 and 20 miles per hour. While the radius
of the central island at Lee Circle is 140 feet and the
radius at Old Colony Avenue and Columbia Road is
only 88 feet, the average speeds of vehicles passing
through the intersections are remarkably similar.

Observations at these two intersections and others
indicate that an average speed of 15 to 20 miles per
hour is safe and that interweaving of traffic can be ac-
complished at this speed satisfactorily. It is believed
that speeds much in excess of 20 miles per hour are
dangerous except where the intersection has been de-
signed along the elliptical form to pass traffic upon a
major route with a minimum of delay, and where cross
traffic is light and turning movement negligible.

Observ ations of actual intersections indicate that
central islands should not be designed with radii of less

76

than 75 feet. At the customary right-angled inter-
section of two 40-foot roadways, a central island
with a radius of 75 feet will allow vehicles to pass
around the island comfortably at a speed of about 20
miles per hour and will also give a satisfactory distance
between the entering streets for the interweaving of
traffic.

Width of rotary driwweway.—In an effort to determine a
logical theory of design for the width of the rotary
driveway, the following formula has been evolved as a
basis from which to work. A symmetrical case is as-
sumed, as shown in Figure 4 and all traffic is assumed
to pass directly through the circle, making no right or
left turns. It is also assumed that traffic streams oc-
cupy the same width upon the circular roadway as
upon the entering streets. This is believed to be the
case in practice. Observations show that there is little
or no tendency for vehicles to cut out and pass each
other while upon the rotary driveway and it has also
been shown that there is little increase in the capacity
of a lane of traffic, measured in vehicles per hour, as the
speed of vehicles increases above 15 miles per hour.
In other words, while a stream of traffic approaching a
rotary intersection might be slowed from an average
speed of 30 miles per hour to an average speed of 15
miles per hour, the capacity of such a lane would not be
materially decreased and there would be no tendency
for the traffic stream to become broader.

PUBLIC

|

Yo |
ea way | ! 5 RY SN
: i! eS
7 ) |
| |
|1000)

Ficure 4.—DIAGRAM ILLUSTRATING REQUIRED WIDTH OF
Rotary DRIvEwAy

At any point where the traffic on the circle is of maxi-
mum width, as between two successive entering streets,
it may be readily proved that this maximum “width is
the sum of the entering traffic upon one-half of the
circle. For example, if we consider one-half of the
entering streets in the accompanying diagram, streets
Nos. 1, 2, 3, and 4, the width of the traffic stream on
the circle just past street No. 4 will be 1,000+1,000+
600 +400 =3,000 cars per hour (here the term ‘width
of traffic stream’ is understood to mean the graphic
width of the band representing traffic density).

ROADS Vol. 18, No. 5
let ¢ designate traffic density upon the entering streets
and T the traffic density upon the circle, the density of
the stream at a maximum point upon the circle may be
expressed as follows:

by hlack bgt icke = aaeln
9

T=

As the ultimate capacity of any street is in general
determined by the number of traffic lanes upon that
street, it seems desirable to express the width of the
circular roadway in terms of the total number of
traffic lanes on the streets entering the circle. If both
entering and leaving lanes of traffic be included, the
total must be divided by 4 instead of 2 to hold the same
relation, as there are as many lanes entering as leaving
the circle. The width of the circular roadway may
then be expressed in terms of the total number of
traffic lanes as follows:

Sum of all traffic lanes
Number of traffic lanes___of entering streets
of circular driveway 4

Any such formula must necessarily be modified in
practice. In any case, it seems desirable to have at
least two traffic lanes upon the circular driveway, one
for cars passing through and one for cars making right
turns. It is also doubtful if more than six lanes are
desirable. Large open spaces tend to confuse drivers
and the traffic pattern tends to lose an orderly channel-
ized form. Widths as great as six traffic lanes require
lane markers, which are objectionable upon the rotary
driveway.

Ourb radii.—Curb radii should in all cases correspond
as nearly as possible to the radius of the central island.
It has been observed that where curb radii are small,
traffic tends to make the turn upon entering the circle
as broad as is convenient, with the result that vehicles
are carried away from the outer edge of the circular
drive, and a large percentage of unused pavement.
results. In Figure 8, F is shown a trafficp attern of
the Old Colony Avenue-Columbia Road Circle in
Boston. This pattern clearly shows the effect of short
curb radu. In this case, approximately 20 per cent of
the total area of the circular driveway was never used
by traffic.

At this point it may also be pointed out that reverse
curves made by curb radu and the outer edge of the
circular drive are ignored by traffic. It is much better
to follow this traffic tendency in design and to eliminate
such reverse curves by making the outer edge of the
drive in effect a square or a polygon, as shown in
Figure 3.

Directional islands.—Directional islands here refer
to obstructions in the throats of the streets entering a
traffic circle, the principal purpose of which is to chan-
nelize the entering traffic and to direct it into the
rotary traffic stream at an oblique angle. The shape
of the island should be such that the entering traffic
is properly guided in its movement and that no vehicle
can break out of line to take an undesired course into
the rotor. This effect is best attained by the use of
triangular islands, which are naturally formed by the
traffic pattern, the base of the island being an are
concentric with the central island and the apex extend-
ing well up into the entering street. The photograph
of Scott Circle, Washington, eDoG. (fig. 5), shows very
clearly the dead space at the entrances of the con-
verging streets which traffic does not use and which

If we | should determine the shape and position of the islands.

acentieeiiniamaa ———

July, 1932

= y &

Ficure 5.—VIiEwW oF Scott CrrcLE, WASHINGTON,

PUBLIC ROADS

D. C., SHowina AREAS UNUSED BY TRAFFIC AT ENTRANCES OF CONVERGING

STREETS

In designing the sides of the islands it is important
to bear in mind the basic principle that in so far as is
possible the routes followed should be the natural
routes of the traffic. The sides should, therefore, be
arcs concentric with the curbs of the entering streets
and so terminated that traffic entering the circle is
released parallel to a tangent to the central island and
traffic leaving the circle is not deflected from a straight
line course, paralleling a tangent to the central island.

The width of pavement necessary between the base
of any one of the directional islands and the central
island should not be greater than that required to
provide for the expected volume of traffic at that point.
In the case of a right-angled intersection of two 4-lane
streets or highways carrying an equal volume of traffic,
the necessary width is two traffic lanes. In this case,
where traffic negotiates a curve of comparatively small
radius, it is recommended that 12-foot lanes be
provided.

For the sake of appearance and permanency, the
directional islands should be constructed of concrete
or masonry curbing, inclosing a graveled or sodded
area. Where the location of the rotary intersection is
such that pedestrian traffic must be provided for, the
directional islands will also function as pedestrian safety
islands and should be so constructed. The surface of
the island should be given a rough finish to insure safe
footing and the end of the island farthest away from
the intersection should be provided with a concrete
buttress or post to protect pedestrians from reckless
motorists. The buttress will also serve to support a
directional sign.

Signs.—In addition to the directional islands, traffic
should be guided in its movement by appropriate signs.
Such signs ‘should serve two purposes: First, as a warn-
ing to approaching vehicles of the rotor which they are
about to enter and the necessity of proceeding with due
caution; and, second, as a means of directing traffic
movement on the rotor. In existing circles this purpose
is usually accomplished by a series of warning signs
upon the entering streets and 1-way arrows at appro-
priate points upon the circle. <A logical system of sign-
ing is indicated in Figure 3.

“Minimum and maximum designs.—In order to illus-
trate the application of the theories developed in the
preceding discussion, two typical designs have been
prepared, one suggested as the minimum desirable
installation, while the other is intended as an example
of the maximum size beyond which no improvement
in operation may be gained.

As the rotary installation requires considerably more
area than the ordinary intersection, the cost of the
extra land will limit the size of the circle at many
locations. The design decided upon will be the result
of balancing the cost of land against the size necessary
for efficient operation.

The design shown in Figure 3 is suggested as the
minimum desirable circle for the intersection of two
4-lane highways or streets and should be applied at a
location where land values are relatively high and
traffic speeds are moderate.

The basic requirement which should determine the
minimum size is the distance necessary for easy inter-
weaving of the vehicles and the angles at which con-

78

PUBLIC

verging lanes approach each other. As previously
noted, the interweaving distance should not be less
than 100 feet for good operation and the angle of
convergence should not exceed 30°. In the present
design, these requirements are satisfied by a central
island 150 feet in diameter as the distance between
any two consecutive directional islands is 100 feet and
the angle between any two conflicting lanes of traffic
is less than 30°.

A central island 150 feet in diameter gives a turning
radius of 75 feet and satisfies the minimum conditions
for convenient operation, permitting a speed of about
20 miles per hour around the circle.

It will be noted that the curb radii are also 75 feet
to correspond with the radius of the central island and
that the outer curbs of the circular roadway are straight
sections joining the curbs of the entering streets. This
facilitates the right turning movement, for the same
speed may be maintained when turning right as when
proceeding through the circle. There is no tendency
to swing out into the traffic upon the circle and all the
pavement area is utilized.

The islands in the throats of the entering streets
occupy the area which would normally not be used by
traffic and are so shaped that they channelize the traffic
movement, but in no way interfere with the natural
routes. The sides of the islands are circular arcs,
24 feet from and concentric with the curbs of the enter-
ing streets, while the base in each case is an are con-
centric with the central island and 24 feet from it.
This allows for two 12-foot lanes on all sides of the
island, the lane width recommended for curves of com-
paratively small radius. The sides of the islands are so
shaped that traffic is released on a tangent to the circle
and appropriate warning and directions are provided.
As shown in the diagram, the roadway is designed to
carry two lanes of traffic on all parts of the circle with
provision for four lanes between entering streets.

The diagram of the possible traffic paths would
indicate 16 possible conflict points. A condition such
as this would probably never exist, even in the heaviest
traffic. For illustration, consider the case of a driver
going straight through the circle. When there were
two lanes moving on the circle, his tendency would be
to remain in the outer lane and to head directly for the
exit street on passing the central island. If, however,
he wished to make a left turn, following around the
rotor for 270°, he would in all probability enter the
outer lane of traffic and at the first opportunity move
into the inner lane next to the rotor, remaining there
until he approached the street on which he intended to
leave the circle. When an opportunity offered, he
would mingle with the vehicles in the outer lane and
leave on a tangent as did the first driver.

If the drivers acted as outlined above, which is a
reasonable assumption, they would cut only the two
lanes of traffic upon the circle and this reduces the num-
ber of conflict points to a possible maximum of eight,
or one for each lane of traffic. There will ordinarily
be but a single line of traffic around the rotor and proba-
bly one on each entering street, thus reducing the
number of conflict points to four.

Since land values and costs fluctuate widely, there
has been no attempt to estimate the cost of constructing
the traffic circle illustrated in Figure 3. However,
the following comparison of the rotary design with an

ROADS Vol. 13, No. 5

ordinary intersection is made, 100-foot rights of way
being assumed for each of the highways:

Ordinary
Item Rotary | intersec- | Excess
tion
Square Square Square
yards yards yards

Gradings22 1 28 22s ose a a ee 6, 400 3, 600 2, 800
Pa VN G2. a oe es eee ee ee Lp CTR 3, 716 3, 600 116
Island ares. see <a ee a eee ee 2, 697 None. 2, 697

Approximately 1,800 square yards of land will be re-
quired in addition to that included in 100-foot rights of
way.

if many cases, where land is less expensive and the
acquisition of extra land at the intersection 1s not an
important consideration, the size of the circle may be
increased to good advantage. In the design suggested
as a minimum, the entering lines of traffic intersect those
leaving at the next street at an angle of approximately
30°. As the diameter of the rotor and the curb radii of
the entering streets are increased, this angle becomes
smaller until at some point the entering and leaving
lanes become tangent to the rotary traffic lanes, as
shown in Figure 6.

a Neat
ha
FLASHING BEACON __—\\"\¥y, | Dinkee
DIRECTION SIGN Mad <00
rn |
Eo

iert tl x

a

~ 6

CAUTION SIGN

FIGURE 6.—RECOMMENDED DESIGN FOR A RoTAary INTER-
SECTION WITH CENTRAL ISLAND OF MaxIMuM DIAMETER

It is obvious that any further increase in the diameter
of the circle will not result in a corresponding improve-
ment in operation. The entering lanes of one street
merely become tangent to the rotary movement before
the exit lanes of the next successive street leave it and,
in addition, it becomes necessary to introduce the
objectionable reverse curve in the outer curb.

The physical features of this circle are designed in
accordance with the general principles followed in the
design of the minimum circle. The central island and
the curbs of the entering streets are of equal radius and
the straight outer edge of the circular roadway elimi-
nates the reverse curve in turning right. The islands
are designed according to the traffic pattern and since
the distance between islands is much greater than is

PR mn

July, 1932

the case of the smaller circle, the roadway width may
be less and still permit easy interweaving.
_ From the standpoint of efficient operation, this circle
is the largest that should be used. There is no conflict
between entering and leaving lanes and with reasonably
skillful driving there should be no conflict of traffic lanes
upon the circle. The only reduction of speed is occa-
sioned by vehicles interweaving and jockeying for posi-
tion. ‘Table 1 indicates that speeds of 30 miles per hour
may be maintained on the circular roadway with com-
fort. A circle of this sort would be rarely installed, but
it may be advantageously used at the intersection of two
heavily traveled rural highways or at such locations as
parkways, civic centers, and the like.

The land required in excess of the 100-foot right of
way is approximately 14,500 square yards, and the
quantities are as follows:

Ordinary
Item Circle | intersec- | Excess
tion

Square Square Square

< yards yards yards
(io GREK RU OYERS ot Baten cA ces ge 27, 800 7, 000 20, 800
1 pla eg es 5 2s ope ee ee 9, 800 7, 000 2, 800
Island area 18, 000 None. 18, 000
CUD in Con aeeeree eee ee FE ee 15,740 13, 120 1 2, 620

1 Linear feet

Adaptability of rotary traffic—In conclusion, it may
be well to point out the advantages of the rotary
traffic system and to suggest the limiting conditions
which will determine the expediency of its application
at a particular location. The greatest apparent ad-
vantage of rotary traffic is that in theory it presupposes
a continuous movement of traffic, direct conflict of
vehicles and the troublesome left turn being eliminated
by the device of compelling all traffic to proceed in one
direction around a circular drive. The system is
capable, therefore, of handling a large volume of
traffic with little delay.

Another very distinct advantage is the reduction in
accident loss. The shape of the true rotary inter-
section is such that traffic is compelled to slow down
and the paths of vehicles do not cross at right angles,
but rather converge and interweave. <Any accident
which occurs, therefore, is the result of a small dif-
ferential of speed, a following car colliding with a
slower vehicle proceeding in the same direction, or
side-swiping a vehicle during the interweaving process.
Head-on collision, or a right-angled conflict of vehicles,
is virtually impossible.

That safety is improved by rotary traffic is evidenced
by Table 2, which gives the experience in Los Angeles,
Calif., before and after the installation of a traffic
circle.

In spite of these obvious advantages there are
several disadvantages which seriously restrict the ap-
plication of rotary traffic in the ideal symmetrical
form. The cost of the excess land required is a signifi-
cant factor where land values are high. It would be
economically unsound, for example, to install even
the minimum suggested design at intersections in the
business district of a city. The cost of excess land at
such a location would be so great that it would probably
be more economical to construct a grade separation.

A second factor is that of topography. Tne rotary
system is designed for operation on level circles and
any attempt to install a rotary intersection on a
grade would result in obvious complications. As far as

PUBLIC ROADS

79

TABLE 2. Number of accidents and property damage before and
after the installation of a traffic circle in Los Angeles, Calif.

Neighboring right-an-
gled intersection at
Wilshire Boulevard
and Vermont Avenue

Intersection at Wilshire Boulevard and Western Avenue

S ‘ Property w Property
1922 Accidents damage Accidents damage
4 months, before installation of
GP ATIC ICING G ee ae ee 50 $1, 491 30 $833
6 months, after installation of |
Ur AM ChCINC] Of aens-eekase eee = 32 353 62 1, 640

is known, there are no installations where the circle
itself is on a grade.

A most important consideration is the character of
the traffic. The system operates to greatest advantage
when traffic is uniform in character, as a variety in type
of traffic seriously reduces its efficiency. It was
intended primarily to facilitate motor-vehicle traffic
of roughly uniform operating qualities. When, in
addition, pedestrian and street car traffic must be
provided for, it is necessary to modify the system to a
considerable extent.

In the usual rotary intersection, vehicular flow is
uninterrupted and the pedestrian is at a decided dis-
advantage. The situation, however, is similar to that
at any uncontrolled intersection and unless there is a
very large volume of traffic, no particular provision
need be made for pedestrians. The auxiliary direc-
tional islands serve as convenient refuges and it is
suggested that pedestrian crosswalks be laid out to
utilize the safety areas thus provided. By using the
islands in this manner, the pedestrian crosses no more
than two or three lanes of traffic at one time, and
encounters vehicles moving in one direction only.

When vehicular traffic is very heavy and when, in
addition, there is a large volume of pedestrian traffic, it
will be necessary to provide pedestrian subways or to
interrupt the vehicular flow occasionally for the con-
venience of pedestrians. This is easily accomplished
by the installation of traffic signals as at an ordinary
intersection.

Street cars present a more difficult problem. In a
ereat many instances where the rotary system has been
applied to regulate traffic on an existing circle or square,
tracks are so located that street cars conflict with the
rotary movement of vehicles, the street cars generally
proceeding directly across the circle. In periods of
hght traffic this conflict is not serious, but as the traffic
volume increases it becomes necessary to interrupt
movement upon the rotary roadway for the passage of
street cars.

Square or polygon-shaped central islands.—The use of
square or polygon-shaped central islands in the design
of rotary intersections reduces the efficiency of the
system and any advantages which may be attributed
to this type of design are enhanced in the circular
design. This particularly is true where the minimum
size of rotor is contemplated for a given intersection.

Figure 7 illustrates two types of rotary intersection
in which a square central island is used, the island
being so designed that the sides of the square are at an
angle of 45° to the center lines of the streets forming the
intersection. The intersection in each case is a simple
right-angled one and the purpose of the designers has
evidently been to evolve a rotor requiring a minimum
amount of land compatible with efficient operation.

80

PUBLIC

COOK COUNTY DESIGN

Ficuret 7.—Rorary INTERSECTION DeEsIGNs WITH SQUARE
CENTRAL ISLAND

The British design appears in A Report on the Lay-
out of Crossroads, Junctions, and Corners, submitted
by the British Ministry of Transport to all road author-
ities in England. This report was published in full in
the The American City for November, 1929, Volume XLI,
No. 5, pages 151-154. The design which appears here
was recommended for use at the crossing of two roads
of equal traffic importance. The Cook County design
is included in the report of the Cook County, IL,
Grade Separation Advisory Committee, August 5, 1929.

The greatest apparent advantage of this type of
design is that it permits better arrangement of the
building lots about the intersection than does the cir-
cular form. However, if the outer curbs of the inter-

ROADS Vol. 13, No. 5
section are designed as straight lines, as suggested in
Figure 3, rather than as arcs concentric with the cir-
cular island, this apparent advantage disappears.
There remains only the possible advantage to be gained
in a saving of land required by the square design.

Table 3 gives a comparison of the dimensions of the
two square designs and the recommended circular de-
sign, showing the various areas of pavement and islands
required:

TABLE 3.—Dimensions of central island and land areas required
for British and Cook County designs, as compared with recom-
mended circular design of Figure 8

Area pave- F Area excess
ment Area islands land taken
: Dimensions of central
Design island

Square| Per |Square} Per |Square| Per
yards | cent!| yards | cent !| yards | cent ?
IBTitishae== aes 110 feet square________- A LGT.| PUL le vel lea 860 47
Cook County-_-_-_| 166 feet square___.____- 4, 224 113 | 2,982 | 110.5 | 2,300 126
Recommended__| 150 feet diameter circle_| 3,716 | 100 | 2,697 | 100.0 } 1,820 100

1 Percentage of recommended design.
2 Excess area required to be taken based on 100-foot right of way in each case.

In spite of the shght advantage in the amount of land
required in the case of the British design, there appear
to be several serious objections to the square design
from the point of view of traffic efficiency. These
objections may be made clear by a detailed discussion
of the designs in Figure 7.

The first objection is the necessity of using a very
short radius in rounding off the corners of the square
island. In the British design, while the square is 110
feet on a side and gives an admirable distance between
entering streets for interweaving, the curves rounding
off the square have a radius of only 30 feet. This radius
is but slightly larger than the minimum turning radius
of our longer-wheelbase automobiles. It is obvious
that in negotiating this rotor traffic will be compelled
to travel very slowly to remain in the channels provided
for it or it will maintain a normal rate of speed and
avoid the designed channels. At a speed of 15 or 20
miles an hour, the vehicles occupying the inner lane
of traffic next to the central island will be thrown
toward the outer lane on rounding the corners, with
resulting conflicts and possible accidents. The traffic
proceeding about the square will tend to take a circular
course and the traffic pattern wil! undoubtedly show the
square inscribed in a rough circle. The 30-foot curb
radu of the entering streets will bring about a similar
effect along the outside of the rotor when vehicles make
aright turn. These two tendencies reduce the effective
width of the roadway and concentrate traffic in the two
center lanes.

The Chicago plan has some advantages over the
English design. The curb radu are 75 feet, and cars
turning to the right with the intention of leaving by
means of the next street can negotiate the turn at
about 20 miles per hour without swinging wide into
the inner lane. However, the design is not consistent
in that the radius of the curves rounding off the square
rotor is only 42 feet. While a night turn can be made
at a speed of 20 miles per hour, a car proceeding directly
through the intersection must slow down considerably
in making the 42-foot radius curves. If speed is not so
reduced, the motorist will be forced to swing out into
the next traffic lane and the same disadvantages hold
as for the English design.

July. 1932
EXISTING TRAFFIC CIRCLES DISCUSSED

In an attempt to gather information concerning the
design and operation of existing traffic circles, a ques-
tionnaire was sent to all cities with a population of
100,000 or more and to other cities in which it was
known that traffic circles were in operation. A sum-
mary of the data assembled through the courtesy of
the various city engineers and members of city planning
commissions appears in Table 4. This table, while
containing all the information received, is admittedly
incomplete, but will reveal particularly the wide vari-
ance in practice in the design of circles. In view of
this fact, several plans are presented, each of which has
one or more particularly good features which, if incor-
porated in a single design, would result in an intersection
almost coincident with that presented in the previous
chapter.

It will be seen in the table that the speed of vehicles
passing through the intersection was given in only two
cases. Despite the wide difference in both the diameter
of the rotor and the volume of traffic, the speed main-
tained is practically the same. It is believed that this
speed will be relatively constant for all circles, but any
additional information both as to volume and speed
which may be maintained upon existing circles would
be very valuable to one considering the installation of
such a design.

Monument Circle—Monument Circle! in Indian-
apolis, Ind. (fig. 8, A), represents good practice in
existing traffic circles. It was originally planned in
1821 by Ralston, an assistant to Major L’Enfant, as
the center of a city 1 mile square with four broad
avenues radiating from it. At the present time, the
circle passes 1,500 to 2,000 vehicles per hour without
interruption and without regulation by traffic officers
or signal-control lights. It is also the terminal of all
city bus lines.

Features of note are the large radius of the central
island and the design of the islands in the entering
streets. These islands were installed in response to
traffic demands and for pedestrian safety. It is worthy
of note that while the areas are merely outlined with
stanchions and traffic buttons, the operation is efficient.

The circular driveway width, which is entirely ade-
quate in this case, is the same as that given by the
formula previously suggested, that is, one-quarter of
the width of the entering streets. The operation of the
circle would undoubtedly be improved by increasing
the curb radii of the entering streets, but there is serious
question if increased efficiency would compensate for
the expense of such a proceeding in the heart of the
city. .

Niagara Square.—Niagara Square, Buffalo, N. Y.
(fig. 8, B), is a good example of the rotary system
applied to a large square. The corners of the central
island have been cut back to such an extent that it
is practically a circle and large turning radii are pro-
vided for traffic circling the island. It will also be
noted that the curbs of the entering streets are cut
back to provide a turning radius sufficient to allow
entering vehicles to execute the right turn without
interfering with the traffic already upon the square.

As there are seven entering streets, the interweaving
distance in several places is less than has been recom-
mended; but because the heavy traffic flow is largely
confined to Niagara Street and Delaware Avenue, the

1 Information furnished by Mr. H. B. Steeg, secretary-engineer, city planning
commission, ,

PUBLIC ROADS

Sl

| TaBLE 4.—Hzisting traffic circles in cities of 100,000 or more
| population in the United States

Total | Width] .. Maxi-| a...
Diam-|width| of sae mum | * oo
. =e eter of circu- ; ve- ;
Circle Location of i Nantere 0 lex po Aieles Soe
circle | ing | road- per
streets} way streets hour hour
Feet Feet Feet
Weeeoe rose sete New Orleans, La._| 280 202 40 4] 3,400] 16-19
Claiborne! 2. =... =, Bey 6ta\2 eae Sans E 210 268 31 (ie (mera S| |p. 2 tee
Druid Hill Park_-} Baltimore, Md_-_-- 115 | 236 85 7 See es Le Sa
INTa gata be fs soe Buitsiow Nie eco 305 | 374 75 io | SRD OO) ae
Monument_--_---- Indianapolis, Ind 333 | 200 50 4. || 2,000". = ae< 2
DUR Onts oro soon Washington, D.C_} 386 464 40 TOG) eons eae
slaty ake Chal se ewes eee (eae CLGira™ uereuee es 190 164 40 Oi aes eee
Thomas. Csie 254 soe! dos Bees Sere 208 440 50 871) spe00! [eae
PCOUbs seco gee eee elt oe aw Oe ae eat eee 120 450 60 6. 27660" ie
LOWSeeeeeee oe eee Ose ere 380 324 36 So eer bOO uence
Washington. —- - 2-22 (3 C0) ating! bc eae 350 360 40 bo fa ek be S| [Ped
TAD Gases ee nee dope 2 Se? 300 300 40 cies [egal [ee ees
PMOL aie. eee | eee CU Gm ee aes 320 300 50 Od] Se |e eee
Lincoln Memorial_|._-_- GOQDEE Ss Seer ee 640 290 60 i ee Seal es Be
OhovyaGhasce en lessee GOL a. eee ee 240 350 70 } gl Rae OB ee
Laurelhurst__-_---- Portland, Oreg___- 190 192 8 Bye ee eS
Central Park____-- hele (aah phere Nall Jo 240 264 36 to) ees [ee
Colorado and | Pasadena, Calif--_- 60 194 70 Cee es ae eee
Orange.
Columbia Road | Boston, Mass____-j 175 177 60 4; 3,000 | 15-20
and Old Colony
Avenue.
Kaign Avenue____| Near Camden, N.J-_ 320 310 50 Gis, 200) |eaee aos
Whitehorse Pike__|_---_ Glo) y= Aa ee 1110 145 45 By |; 2ra6o: (2a oo
Brooklawn East__| Near Brooklawn, 200 167 36 Le eee Bea aoe
Brooklawn, West_|.---. (clo ere Le eS 155 135 33 Sih Poe Sao a ees Se
Ridge Road Bridge | Rochester, N. Y-- 216 300 60 Giles eae =| See
approach.
Lindell (proposed) | St. Louis, Mo___-- 130 320 70 Sit) ee Ae ee

1 Minimum.

operation of traffic through the square is not seriously
affected. Here the width of the circular roadway is
less than the maximum given by the formula and this
width is still further reduced by vehicles parked around
the outer curb, illustrating that the formula gives a
very generous roadway width and that traffic can be
handled efficiently with less width.

A traffic count made on July 7, 1929, showed that
3,548 vehicles entered the square during the maximum
hour and passed through without delay or confusion.”
The advantages of the design are the large radii of the
central island and the curbs of the entering streets.

Circles in Portland, Oreg—Two traffic circles of
Portland, Oreg., present examples of good design.
Figure 8, C is the intersection of two main traffic streets
in a residential district. Both carry a large volume of
traffic which passes through the circle without inter-
ruption.

An interesting feature of this design is the excep-
tionally large radu of the curbs of the entering streets.
A radius of 200 feet gives a continuous curve for traffic
turning right from one entering street into the next
and results in the outer curb of the circle being convex
with respect to the central island. Where land is not
exceptionally expensive, this practice offers some ad-
vantage over the straight outer curb design. Very
little roadway width is wasted and vehicles are en-
couraged to follow a natural route. The radius of
the central island is 95 feet, resulting in a satisfactory
interweaving distance.

Figure 8, D illustrates a treatment where a number of
streets converge at a point. The radius of the central
island is too small to give a satisfactory interweaving
distance provided all the streets were carrying a heavy
traffic load, but it is effective in this case because the
traffic is concentrated on Ladd Avenue and the other
streets are of comparatively minor importance.

2 Report of the Committee on Street Traffic Economics, Bulletin 104 of tha
American Railway Association, p. 28.

82 PUBLIC ROADS

Vol. 18, No. 5

/
5

ST.CHARLE

C. TRAFFIC CIRCLE IN PORTLAND, OREGON. D. TRAFFIC CIRCLE IN CENTRAL PARK , 5 WEE CIRCE

PORTLAND , OREGON .

F. COLUMBIA ROAD CIRCLE, BOSTON, MASSACHUSETTS.

Figure 8.—EXAMPLES OF EXISTING

TO WHITE HORSE PIKE =X
G. KAIGHN AVE. ROND POINT, NEAR CAMDEN, NEW JERSEY.

TRAFFIC CIRCLES

ee ee

July, 1932 PUBLIC

In both these designs excellent results are obtained
with a roadway width less than the theoretical maximum,
three lanes of traffic being provided in the first case and
four in the second. Directional islands might well be
added in the design, being particularly adapted in the
first case where the open space in the entering streets
created by the large curb radii is likely to prove con-
fusing to entering traffic and hazardous to pedestrians.

Lee Circle-—Figure 8, E is a drawing of Lee Circle in
New Orleans, La., which has a diameter of 280 feet.
The short curb radii necessitate a reverse curve move-
ment through the circle. This condition gives rise to
a large area of unused pavement and makes improb-
able the desirable flat angle of intersection. However,
the large diameter affords a greater interweaving dis-
tance, a desirable feature.

Traffic counts taken for the entire circle show a total
of 2,543 vehicles entering the circle during one hour.
Partial counts during the peak period indicated that
nearly 3,400 vehicles passed through the circle during
the rush hour. Speed studies showed that the speed
varied from 16 to 19 miles per hour.

The roadway width in Lee Circle is 40 feet which,
with a parking lane, permits three lanes of traffic.
The total number of lanes on the entering streets,
subtracting parking lanes, is 13. Thus the width is
slightly under the maximum given by the formula sug-
gested. The fact that there was at all times a complete
freedom of movement in spite of the disadvantage of
the short curb radii indicates that the formula gives a
reasonable maximum width of roadway.

Columbia Road Circle-—This circle, near Boston,
Mass., is represented in Figure 8, F. It is very near
the minimum recommended design, having a central
island 175 feet in diameter. It is located at the inter-
section of Old Colony Boulevard and Columbia Road
and at certain times of day is required to accommodate
a large number of vehicles with a large percentage of
turning movements.

The effective operation of Columbia Road Circle,
even under its peak loads, is a proof of the efficiency
of this type of design. Observations indicate that well
over 3,000 vehicles pass tbrough the intersection dur-
ing a peak hour at speeds ranging from 15 to over 20
miles per hour. During these observations congestion
was not appreciable, no actual stoppage was ever seen,
and little slowing down below the speed required for
comfort in turning was noticed, even in periods of heavy
traffic,

This circle further indicates the unused area created
by the circular outside edge of the roadway. Traffic
patterns on the pavement show that over 20 per cent
of the pavement is never traveled over by vehicles
passing through the circle.

Kaign Avenue Rond Point.—This circle, shown in Fig-
ure 8, G, was constructed by the New Jersey State
Highway Commission. It has for a rotor a perfect
circle, the large radius being necessary to provide for
a proper interweaving distance.

It will be noticed that close attention has been paid
to detail and that all details, in themselves correct, are
properly combined to form an efficient intersection
design. It is this attention to detail that premits the
effective operation of this circle under the conditions
of heavy traffic, a maximum of about 3,000 vehicles
per hour being passed with little delay.

In the preceding designs no effort was made to pro-
vide for unbalanced traffic flow. The designs shown
in Figure 9 are intended to illustrate the flexibility of

ROADS 83

the system, to suggest a modification applicable to the
intersection where it is advisable to give preference to
the traffic upon one or the other of the intersecting
streets, and to suggest a rotary treatment for the com-
mon forked intersection.

It will be noted that each of the designs applies the
basic principles on curb radii, island location, and inter-
weaving distance previously developed. Figure 9, C
shows how even a common parkway may be developed
on rotary principle, which results in a design similar
e pe applied by Mr. Fritz Malcher in Radburn,

SPECIAL DESIGNS WITHOUT ROTARY PRINCIPLE

The rotary principle is a specialized type of treat-
ment which is particularly well adapted when a large
volume of traffic must be handled at a comparatively
low rate of speed. At intersections where there is only
an intermittent flow of cross traffic, the vehicles upon
the main highway are unduly penalized by the shape
of the rotor. While the rotary system is not well
adapted to such a situation, some form of treatment is
desirable to permit the high speed boulevard traffic to
flow without interruption and at the same time to pro-
tect the traffic crossing the main route and that turning
into it from the minor route. The following designs
have accordingly been presented to illustrate how this
purpose may be accomplished by means of a system
of well-placed channelizing islands.

The design in Figure 10, A, is well adapted to a T
intersection where the traffic entering the heavily
traveled street is very light. This type of intersection
was developed by the Westchester County Park Com-
mission and has proved very efficient at various inter-
sections on the Saw Mill River Parkway. In this design
the main roadway is 40 feet in width and, as shown, the
opposing traffic is separated by islands at the intersec-
tion and the half roadway width increased to 30 feet.
The widening effect is accomplished by means of re-
verse curves so flat (8° in this case) that there is no
cause for reduction of speed on the main route.

The purpose of the islands is not to produce a rotary
movement, but rather to provide a safety zone for
vehicles waiting to enter or leave the main traffic by
means of a left turn. For right turns, either entering
or leaving the side street, 40-foot curves are provided
and the increase from 20 to 30 feet in the half roadway
width permits the turning vehicle to proceed alongside
the main stream of traffic until it can accommodate
itself to the speed of this traffic. In the case of left
turns the importance of the islands is shown to best
advantage. In turning left into the through street,
the driver waits in the entering street until there is a
sufficient interval in the traffic stream to allow him to
cross to the space between the islands. If necessary,
he may wait again in this protected area until the lane
next to the island is open, when he enters and remains
close to the island as he accelerates to the speed of the
main traffic. During this acceleration period, there
is still 20 feet to the right of the vehicle as it follows the
island and there is ample room for all vehicles to pass
even though both lanes are flowing full.

Similarly, in making a left turn from the main street
into the side street, the driver remains close to the other
island as he decelerates, thus leaving room for two
lanes to pass on his right. Having slowed down sufh-

3 Abolishing Street Traffic Intersections Without Grade Separation by Fritz
Malcher ,American City ,September and October ,1929.

84

PUBLIC

ROADS Vol. 13, No. 5

A. DESIGN FOR ROADS OF UNEQUAL CAPACITY

Oe
jp ZS :
RS, tee ie oa,

~

a i se
Bole ote
SP GM Me eH oth
Gea a \

C.DEVELOPMENT OF A PARKWAY FROM A ROTARY TRAFFIC CIRCLE

— =

KE

L

40'

_8° REVERSE

B. INTERSECTION OF A THROUGH ROAD WITH AMINOR ROAD

ae

E FORKED INTERSECTION WHERE BOTH STREETS ARE OF EQUAL IMPORTANCE

F. SUBSTITUTION OF A CONNECTING ROADWAY
FOR A ROTARY TRAFFIC CIRCLE

FIGURE 9.—SpPECIAL ADAPTATIONS OF THE RoTary PRINCIPLE ~

ciently, he turns into the protected area and as soon as
the opportunity arises, crosses the other half of the
highway and proceeds on the side street.

A design of this sort is less rigid in its various re-
quirements than is a rotary traflic circle. Since no one
will turn completely around an island, there is no
necessity for making it the usual 60 feet in width. It
is sufficient to place it so that it will be just inside the
path followed by a vehicle in making a normal left
turn as indicated by the traffic movements. Thus, the
width is a factor only of the space required to provide
an adequate safety zone. In this case 14 feet is used, |

a width which has been found satisfactory. Since a
vehicle waiting in the protected area will stop at some
point in its normal turning path, it will be in a diagonal
position to the roadway at an angle of approximately
45°, so that 14 feet is ample to protect the largest car.
The width of the narrow end of the island and its
length are immaterial, the sides of the island generally
being concentric with the sides of the road and the
limiting condition at the narrow end being the width
necessary to protect properly a significant warning sign.

No extra land is required over the normal right of
way. An estimate of the quantities follows:

July, 1932 PUBLIC
. Ordinary
Item Fite inter- Excess
g section
Square Square Square
yards yards yards
(Cpurta hea teg pa aes Ape os eee Lg ATS aes Aer gs 3, 670 2, 570 1, 100
PAV IOC Cee ote en poet Shesebe seta tewn cease aan eren 3, 470 2, 570 900
MIAO AT Ott aera is Ree eee AR Lo 200 0 200
Petree ee ae aie SO Sen Sin cote oan pemaee 1435 0 1 435

1 Linear feet.

The design shown in Figure 10, B, is very much the
same as that discussed for stub-end intersections.
This design, it may be observed, is applicable to the
intersection resulting when a lightly-traveled street
enters a heavily-traveled main highway on a curve and
approximately tangent to the curve, a case very often
encountered.

The physical features of this intersection follow
exactly the same principles as those developed for the
T intersection. In this case, the desired extra width
is obtained by flattening the curve of the inside edge,
and providing curves of greater degree on the outer
edge. To eliminate a reverse curve on entering the
main road from the secondary road and to prevent a
vehicle from encroaching on the traffic lanes of the main
road before it has acquired sufficient speed, the outer
edge of the secondary road should be brought in on a
tangent to the widened curve from a point some dis-
tance back of the intersection as shown in the diagram.

The effectiveness of the operation of this intersection
depends entirely upon the proper location of the islands
which, in turn, depends upon the radius of curvature
and the angle of intersection. The details of the loca-
tion of these islands may be seen in the diagram.

With the usual rights of way now acquired for rural
highways, this design does not require much excess
land. Assuming 100 and 60 foot rights of way, respect-
ively, and that the present roadways are centered on
the center lines of the rights of way, 2,500 square feet
of excess land will be required, consisting of a small tri-
angle in the throat of the intersection. When the de-
sign is to be constructed in conjunction with a reloca-
tion of the highways under consideration or in conjunc-
tion with new construction, the center lines of the high-
ways may be so placed with respect to the rights of
way that no extra land is required.

The design in Figure 10, C, another adaptation of the
Westchester system, is similar to that presented in Fig-
ure 10, B except that the minor street is the one requir-
ing the turn instead of the major street. The basic
principle is the same; the turning traffic is protected
from the through traffic and can not inconvenience it.
Extra highway width on either side of the islands per-
mits the slower turning traffic to mingle freely with
the fast through traffic and an ample protected area
between the islands is provided for waiting if necessary
before turning.

The feature to be noted is the difference in the loca-
tion of the safety islands. As in the previous design,
they are so located that traffic turning about them will
be directed into the proper route, but because of the
difference in angles and the straight instead of curving
through highway, the distance between the islands is
much less. This indicates the necessity of a study of the
particular intersection before placing the islands, since
their proper location is the determining factor in the
successful operation of this type of intersection treat-
ment.

ROADS 85
“Oo .
: Sa ae
+ - oO
100- 0 “2
8° REVERSE
CURVE

B. DESIGN OF FORKED INTERSECTION WHERE ONE
STREET 1S OF MINOR IMPORTANCE

C. DESIGN OF FORKED INTERSECTION WHERE ONE
STREET !S OF MINOR IMPORTANCE

Ficure 10.—Sprcrat Destens WitHout Rotary PRINCIPLE

The extra land required is negligible and, as the
additional pavement is dependent on the angle of inter-
section, no specific estimate is presented. In any case,
the quantities will not be much in excess of those for
the stub-end, right-angled intersection. (Fig. 10, A.)

EXISTING SPECIAL DESIGNS

The designs presented in the preceding paragraphs
were not intended to cover all possibilities, but rather
to bring out the principles involved and to show their
application to a few common types of intersection.
The designs illustrated in Figure 11 show how, in some
cases, these principles have been actually applied and,
in others, the proposed application. Each design rep-
resents a carefully considered solution of the particular
problem and is illustrative of a practice which might
well be applied at countless intersections.

The three designs shown in Figure 11 A are in
Miami, Fla., and represent a good application of the
principle that the driver should be directed into the
proper route by making that route the natural one.
The first of these (N.W. Fifth Street) might be termed
a modified rotary system, in which case the central
island would be a rotor, about which the streams of
traffic flow, vehicles entering or leaving as the line
progresses. In a sense this is what actually happens,
but because of the general layout of the intersection
and the turning movements to be expected, it is prob-
able that most of the traffic will turn about the island
rather than follow it closely for any considerable dis-
tance, as in a true rotary movement. For this reason,
therefore, this design is classed as a special design and’
all the islands are termed directional islands.

The traffic entering the intersection from any street
is confronted by the “oval island, about which it must
turn. The island is so placed that any vehicle follow-
ing its natural course through the intersection inter-

S86 PUBLIC ROADS

N.W.11 th ST. + -— ee
WE Se ae Ser Lies Os
Sy NW.11 th ST,
: Of ze ee
> \
\ } | = vs
NSE Ze Nev
ee ee
\
« te
\/ v S|
/ Z
Ww
|
z 3 a
| 4
uge zt
fae
Sera =
zac Zz

NW.4th ST

LEGEND
~< — TRAFFIC LANES
* STREET LIGHTS
° LIGHTS ON CURB

A ISLAND DESIGNS USED IN MIAMI, FLORIDA

Vol. 13, No. 5

NEWroy, s

B. PROPOSED DESIGNS FOR INTERSECTION OF SOUTH AVE.,
NEWTON ST. AND PARK ROAD IN WESTON, MASS.

SEPARATION OF TRAFFIC LANES ON CURVE, WITH PROVISION FOR
MINOR INTERSECTION, BUS STOPS, AND U TURNS

4 op
“3 Borve® =
ce BUS ie eae |

4 b+— 175! 40°

t t

BORDER ROAD AND BUS STOPS

200'- -

°
R=
|
XY
oS)

C. DESIGNS USED ON MT. VERNON MEMORIAL HIGHWAY

Figure 11.—Existine Sprcrat DEsians

sects other lines of traffic at an oblique angle, which
makes interweaving or intermingling easy.

The second design (N.W. Eleventh Street) represents
the solution of a rather complicated intersection, the
open areas of which, without directional islands, would
cause confusion. The largest of these islands is a circle
40 feet in diameter. As in the preceding case, this
might be termed a rotary traffic island, but its small
size and the fact that again few vehicles follow close
to the edge for any considerable distance leads to its
classification as a directional island.

Its location is the most important feature of this
design, for upon this depends the routing of all traffic
passing through the circle. The other islands serve
to make vehicles approach the circular island at the
proper angle. The two smaller islands at the east of
the central island provide safety for traffic turning left
from NW Eleventh Place, and prevent any vehicles
from cutting to the left of the circle as they emerge
from NW Eleventh Street.

The third design (NW. Fourth Street) is composed
of strictly directional islands, there being no semblance
of rotary movement. The islands are so shaped and
located that the route which any vehicle should follow
is obvious and is the one which will cause the minimum
of confusion in the intersection area.

In all these cases the islands are of permanent con-
struction, all being curbed and planted with grass,

shrubs, or palms which add measurably to their appear-
ance. It is of interest to note that they were not in-
stalled as permanent fixtures until the size and shape
had been determined by trial, using temporary islands.
In this way it was possible to insure efficient operation.

The following excerpt from a letter from Mr. J. E.
Jewett, office engineer, is of interest:

There is little question but what such traffic islands reduce
accidents very materially. Rotary traffic is usually slow traffic
in terms of miles per hour, but is rapid traffic in terms of vehicles
per hour. As traffic congestions develop, we expect to install
more such traffic separators.

We have learned that we can seldom lay out a system of islands
in the office that will work. It is nearly always necessary to
make changes in the field. Our policy is to put up movable
forms for the islands, making changes here and there until we
are convinced that we have solved the problems. These forms
are a in place as long as 30 days before the permanent curbs
are built.

Figure 11, B represents two designs prepared for the
intersection of South Avenue and Newton Street in
Weston, Mass. The upper plan shows an adaptation
of the design presented as the Westchester type to the
special conditions encountered here. The islands are
so shaped and located that they direct traffic into the
routes consistent with the most efficient operation of
the intersection. No traffic lines are materially devi-
ated from their natural courses and ample area between
islands provides for the safety of the turning traffic.

at lial

July, 1932 PUBLIC

A more elaborate solution, which would be justified
only in case of a marked increase of traffic on both
routes, such that the consequent delay is considerable, is
seen in the lower plan. This design, similar to Figure
9, E provides a rotary movement, and necessarily
functions well only at relatively low’ speeds.

It should be noted that the second design might be
considered an extension of the first, the throat of the
intersection being practically the same in both cases.
Allowance in a design for future development is an
important feature.

PROGRESSIVE DEVELOPMENT OF AN INTERSECTION

In view of the tremendous cost of acquisition of land
at a date when traffic demands require an intersection
treatment, it is an increasing practice to obtain control
of sufficient land abutting intersections to allow pro-
gressive improvement.

Various means of reserving this land for future use
are exemplified by the methods used in city planning
control of new developments. The simplest and most
effective method is by outright purchase at the time
of initial construction, based on the theory that it costs
little more to obtain a wide strip of land than a narrow
one, but that to take additional land after the original
route is laid out is invariably expensive.

An alternative is to purchase immediately only the
land necessary for the first development of the inter-
section; and, by means of zoning regulations, to insure
against private developments in the right of way to be
needed in the future. Such regulations must neces-
sarily conform to court decisions on the subject of
zoning in the jurisdictions concerned. A reasonable
restriction would allow the owner to make whatever
use of his property he desired, so long as he complied
with the general zoning requirements, but would stip-
ulate that any buildings or other improvements would
be removed from the area in question, without com-
pensation to the owner, at the time anticipated for the
improvement of the intersection. This would permit
the erection of inexpensive buildings having a length
of life less than the period between the first and the
second improvements, as well as the use of the land for
agricultural or other purposes. It would, on the other
hand, prevent the building of permanent structures
which would preclude the possibility of a grade sep-
aration or a traffic circle.

Where zoning acts do not permit this procedure, it
may be possible to incorporate in the deed covering the
original purchase a provision similar to the restriction
outlined above, applying to land which will be required
for future intersection development.

In case all the land required for full development of
the intersection is purchased at the time of initial con-
struction, the land not needed immediately may be
leased for the construction of temporary buildings or
such other use as may be profitable. In this way all
or part of the carrying charges on the additional land
may be defrayed during the period when it is not needed
for the intersection.

If this plan were followed a State highway depart-
ment or other agency would find itself with a consider-
able amount of land on its hands for which it had no
particular use at the time but which must be kept in
a presentable condition.

development of an intersection are presented.
The intersections fall naturally into two classes
according to location, first, those in country or park-

In order best to use the avail- |
able area, the following methods for a progressive |

87

ROADS

way locations and, second, those in districts which will
be built up with industrial or commercial structures.

In the first instance, a proper design would be one
requiring a generally square plot of land with the
intersecting roads forming its diagonals. To provide
for any desired future construction, this square should
be about 425 feet on a side, its corners being located on
the center lines of the right of way about 300 feet from
the intersection of the center lines. Assuming that
this amount of land is taken at the intersection of two
newly designed routes, it is of interest to follow the
possibilities of the layout of the intersection through
increasing traffic stages, as indicated in Figure 12.

The first design shows the crossing of two 20-foot
roadways. The intersecting edges are rounded at a
30-foot radius, but otaerwise nothing need be done.
As the trafic becomes heavier or more flexibility of
movement is desired, it may be desirable to increase
the roadway widths to 40 feet or two lanes in each
direction, but it may still be unnecessary to provide
any special intersection treatment. If turning traffic
becomes a factor and left turns as well as right turns
complicate the traffic, turning roads may be beneficial.
Roads such as these are now installed as a component

GRADE SEPARATION

FIGURE 12.—SuGGEsSTED DESIGN FOR THE PROGRESSIVE
DEVELOPMENT OF AN INTERSECTION

88 PUBLIC
part of many intersections, but usually are laid out
in a circular arc, of perhaps 200-foot radius. The reason
for selection of the straight turning roads is apparent,
however, on inspection of the solution for the next stage,
a rotary traffic circle.

When traffic becomes so heavy that traffic signals
would be necessary to reguiate the right-angled cross-
ing, a rotary design is very effective and, in this case,
inexpensive. The turning roads already constructed
will form a part of the circular roadway and a central
island of 150-feet radius may be laid out in the area
inclosed by the turning roads. The radius of the throats
of the entering streets will be increased, for though in
the previous case only turning traffic used the diagonal
roads, now all traffic swings right on entering the inter-
section and follows around the rotor. It may be seen
that there is ample area to provide a traffic circle which
will fulfill every specification developed in the section
on rotary traffic.

Tn the case when the traffic demands become so great
that the rotary traffic circle will cause an economic loss
due to the required reduction of speed of vehicles pass-
ing through it, a grade separation may be justified.
When this installation is completed, it will be found
that the diagonal roadways which were first classified
as turning roads and then as an integral part of the
circular roadway of the traffic circle have now become
access roads for a grade separation and the two inter-
secting streets again pass straight through the inter-
section, but at different elevations.

Figure 13 shows a clover-leaf grade separation at
the intersection of U. 8S. Route 1 and the Mount
Vernon Memorial Highway. ah

The foregoing discussion outlines a possible intersec-
tion development from the simplest to the most elabo-
rate, each stage of which fits as nearly as possible with
the next and eliminates almost altogether the too preva-
lent factor in highway work, depreciation through obso-
lescence. Proper foresight will eliminate much unneces-
sary expense in solutions which are worthless after a
short period. It is by no means compulsory that each
step be followed in order, but it is extremely unlikely
that the traffic demands at any intersection will war-
rant a transition from the initial to the final solution in
one step and if a progressive, flexible development in pro-
vided for, much expense and inconvenience may besaved.

The second case, that in which the intersection is in
a district expected to be closely built up, does not so
readily adapt itself to a progressive development. It is
for an intersection such as this that the Cook County
Grade Separation Committee recommended a set-back
line 60 feet on either side of the center line for a dis-
tance of 660 feet back of the intersection. As in the
preceding case it is not necessary to proceed at once
from the simple intersection to the final solution, but
rather to follow a series of steps which, though not
developing one from the other as did those in the out-
lying intersection, have a definite relationship with one
another.

Again, there are the two narrow intersecting road-
ways and an equal or greater amount of excess land
not in the form of a square, but instead shaped like a
huge cross, the center lines of which are the center
lines of the intersecting roadways. In this case, also,
the second step may well be the widening of the two
roadways to four lanes each, merely rounding the inter-
secting edges with 30-foot curves. As turning traffic
needs to be better accommodated or as the necessary
stoppage by control devices interferes with the freedom
of right turns, a splaying design becomes appropriate.

ROADS Vol. 13, No. 5, July, 1932

Figure 13.—GRADE SEPARATION AT THE INTERSECTION OF
U. S. Rovure 1 wita tHe Mount VerRNoN MEMORIAL
HiIGHWAy

Here is an admirable opportunity for installing the sep-
arated lane splaying feature, since land is available both
on the sides and for a sufficient distance back of the
intersection. As the traffic becomes even heavier, a
second line may be filled in between the through pave-
ment and the turning lane to increase the storage capac-
ity and in this way increase the efficiency of the inter-
section somewhat. Following this comes the final step,
a complete separation, effected by carrying the middle
four lanes of one roadway under the other.

In this development one feature does not become an
integral part of the succeeding feature. The only pos-
sibility is that the turning lanes introduced by the
splaying may serve as turning roadways for the separa-
tion. It is quite possible, however, during the construc-
tion of a project such as the grade separation structure
and approach ramps that the existing pavement would
be seriously injured and in this event the outer paving
would also be relaid.

Thus, even though successive designs may not lead
to the construction economies resulting from the park-
way development, a proper program of construction
related to the traffic needs will result in an intersection
effective at all times.

Both the preceding cases are concerned with the
intersection to two approximately equally traveled
highways. Another case which very often arises is
that of a major, heavily traveled, highway crossing
several other highways carrying different volumes of
traffic. This case, too, is well worth considering from
the point of view of progressive developments. One or
more of the intersecting highways may have traffic
sufficient to warrant a grade separation or rotary traffic
circle immediately while others, though not now critical,
may in time carry such a volume of traffic that their
intersections necessitate some special treatment and
still others obviously may never have enough travel
to warrant an elaborate intersection design. It will
be found that in every case where the volume of traffic
to be expected some years hence can be estimated,
some progressive plan can be well adapted to the inter-
section. Various designs have been presented for the
intersection of roadways having different volumes of
traffic and all of these designs have been built up from
the same fundamental principles; so it is only a method
of applying the pertinent designs and providing a
means of evolving one from the other as traffic increases.

O

:
'
;
f
t

ROAD PUBLICATIONS of the BUREAU OF PUBLIC ROADS

Any of the following publications may be purchased from
the Superintendent of Documents, Government Printing Office,
Washington, D. C. As his office is not connected with the
department and as the department does not sell publications,
please send no remittance to the United States Department of
Agriculture.

ANNUAL REPORTS

Report of the Chief of the Bureau of Public Roads, 1924.
5 cents.

Report of the Chief of the Bureau of Public Roads, 1925.
5 cents.

Report of the Chief of the Bureau of Public Roads, 1926.
5 cents.

Report of the Chief of the Bureau of Public Roads, 1927.
5 cents.

Report of the Chief of the Bureau of Public Roads, 1928.
5 cents.

Report of the Chief of the Bureau of Public Roads, 1929.
10 cents.

Report of the Chief of the Bureau of Public Roads, 1930.
10 cents.

Report of the Chief of the Bureau of Public Roads, 1931.
10 cents.

DEPARTMENT BULLETINS

No. 136D .. Highway Bonds. 20 cents.

No. 347D . . Methods for the Determination of the Physical
Properties of Road-Building Rock. 10 cents.

No. 532D .. The Expansion and Contraction of Concrete
and Concrete Roads. 10 cents.

No. 583D . . Reports on Experimental Convict Road Camp,
Fulton County, Ga. 25 cents.

No. 660D . . Highway Cost Keeping. 10 cents.

No. 1279D . . Rural Highway Mileage, Income, and Expendi-
tures, 1921 and 1922. 15 cents.

No. 1486D . . Highway Bridge Location. 15 cents.

TECHNICAL BULLETINS

No. 55T .. Highway Bridge Surveys. 20 cents.

No. 265T .. Electrical Equipment on Movable Bridges.
35 cents.

MISCELLANEOUS CIRCULARS

No. 62MC .. Standards Governing Plans, Specifications,
Contract Forms, and Estimates for Federal-
Aid Highway Projects. 5 cents.

No. 93MC .. Direct Production Costs of Broken Stone.
25 cents.

No. 109MC . . Federal Legislation and Regulations Relating

to the Improvement of Federal-Aid Roads and
National-Forest Roads and Trails, Flood
Relief, and Miscellaneous Matters. 10 cents.

MISCELLANEOUS PUBLICATION

No. 76MP .. The Results of Physical Tests of Road-Build-
ing Rock. 25 cents.

REPRINT FROM PUBLIC ROADS

Reports on Subgrade Soil Studies. 40 cents.

Single copies of the following publications may be obtained
from the Bureau of Public Roads upon request. They can not
be purchased from the Superintendent of Documents.

SEPARATE REPRINT FROM THE YEARBOOK

No. 1036Y . . Road Work on Farm Outlets Needs Skill and
Right Equipment.

TRANSPORTATION SURVEY REPORTS

Report of a Survey of Transportation on the State Highway
System of Ohio. (1927.)

Report of a Survey of Transportation on the State Highways
of Vermont. (1927.)

Report of a Survey of Transportation on the State Highways
of New Hampshire. (1927.)

Report of a Plan of Highway Improvement in the Regional
Area of Cleveland, Ohio. (1928.)

Report of a Survey of Transportation on the State Highways
of Pennsylvania. (1928.)

Report of a Survey of Traffic on the Federal-Aid Highway
Systems of Eleven Western States. (1930.)

A complete list of the publications of the Bureau of Public
Roads, classified according to subject and including the more
important articles in PUBLIC ROADS was printed in PUBLIC
ROADS, vol. 13, No. 3, May, 1932. Copies of this list may
be obtained upon request addressed to the U.S. Bureau of
Public Roads, Willard Building, Washington, D. C.

Z€61 > 391440 ONILNIYd INFWNYFAOS ‘SN

thee eeeeeeeowiot

see e eee eet vmWH
eee + OM IROAM
ee0 NIBNOOSIM
se PeWINIDUIA 183M

JO LONI HSM
ees “*WINIDUIA
tere ee eee eLNONUBA

Settee eee eeoonvin
Coe eereeeescguxay
seeeeeeeuaeeRNND!

++" *wLowvg HLNOg
***¥NITOWVD HLNOg
****sONVIe| BOOHY

++ 9 °WINVATASNNZd
eee ++ *Noe3¥Q
tree ee + WMOHYINO

steerer eee ee rQtHg
+e 89 *WLOMWG HLUON
***WNITONWD HLYON

on =O A MBN
see 5***O01X3W MAN
to" *ARBM3P MAN

**SyHSGNVH MBN
** *WOVAIN
+o 9° *wHevEeaN

* *WNVLNOW
***1uNoesIW
**1 ddI GSISSIW

+++ *vLOS3NNIW
sees NYO THOIW
*SLLISNHOVESYW

+989 SONVIARYW
settee eee anNiWW
sess eYNVIBINOF

+8688 * AWONANEH
theese s seveNvy
seeeeeeeesoumo]

sete ees ewNvION|
Sheisivie’*@ 1 ONI77 |
theese ees onwa|

seseee evi ouoag
**waiuon4
Suvav73aQ

**1M9D1LO3NNOD
0 *oavu0109
***WINYOSITVO

IOUS SYSNVXYY
oeoee *WNOZ Iuy
tee eee ee ene

13°306‘GEE*4h
lerbiltogt
25°36‘ f32
1S°091 ‘3866

1G°690‘LOO't
ol*Lle‘Liga's

aaaeteeg
“969°

Cy eoe ont
20°9S6‘SLL

26°26 S18
£1eg9o‘9le‘t

pee
iE *Cel‘ les
G¢*los‘sel‘¢

4S *2t0'0S2 ‘2
9S°1S3‘lés
16°St6 ‘369

en's9e‘£SS
le*nl6‘98
1G °9t6 ‘63 *b

on*l92 ‘Sone
13°209'L9S
26°9L6'2S1'S

36 "926'2Gn‘2
LL*119'2z09

of *t96's
26*2le*Let
Bh 80h‘ Lee

to*gsl‘esi't
t€*100'L9S
66°G8S‘138

20 "HOLS ise
IG*ing ‘Oleh
S°B10 ‘SHE

£o*6n6*SHe*h
CL *HLb tHS'2
2s*Ont'Lgt

1S*2Sh ‘06k
69°£09‘LS0*2
£296 *2k
¢e*LoS‘egt*2
an c6S tend
he “N69 '69n°S

SLO3PO8d MSN
403 FISVIIVAV

SONNY OCl¥-WWY3033

30 30NVIV8

60th 2

B°gt
2°92
9°62
2°9

Grit
6°22

OAM SGAK ata

Aur Ore

° . .
MU Pwo

[ave}
=

. . .

4 cer s

st tIOE FM Mt TMM HMMS
.

rn

=

Qbb6ne ‘tH 10‘82

*ANGNZAOUGNE TWILINE SHL NI G301A0Ud SVM NWHL 3dAL YBHOIH 2O 30vsUNE VY 40 NOILONYIBNOD BHi 40
HONS ‘TIweaNzIo NN]

1$°081'969 ‘09

BLBIGNOD HYOM IWNOILIOOY

*GIV WH83034 HLIM G3IAOUANI ATSNOIARZUd BLOZCOUd NO 3NO0 WYOM TWWNOILICOV OL 843434 NOILONYLBNOO BOVIS MYSL BH{ (+)

sae Pe
1°G6G ‘nh
00 *00t 2h
6L thd ‘ect

00008 ‘£ 12
tS °£33 ‘862
1° 608 'f

26" 111 ‘S69
"961 ‘208 ‘1
ey 19n 9st

he°ls6‘LSt
00°000 ‘0S

10°216'1S8'2
9£°s92e'H98
20°6SE ‘113

£S°On2 ‘one ‘2
22°91S‘C16
9°91 ‘0St

00 *00S ‘29n*2
03 °6£0‘319
33 °0S9 ‘96h

f° 10S *£69
G3 °3h0 ‘Shs

29°C£0'9£
foe ts bee
19°300‘3S

00 "008 ‘622
00°0£9 ‘Gee

49 °6Sr‘ 169
Beg
2k°91G ‘ge

13°991'G2S
£9°GHE‘9SN A
£o"h26‘2l0*t

2e°etl*26l
Go*ntr‘69S‘t
cerigl isl

2l*ote‘ls
en 99l' Let
00*2e92 ‘fh

96°LL6‘f9e
25 °3Sh' Ih
6L°249 St
06°96L‘ toe
te 6Sn'f

21°300‘OnL
0£°610*S02
Co*HLB Oreste
09 "tos ‘£32

1o*S92'61S
9n°£S0*HSl
Go*sig'l

99 °0S9 ‘Ln
19 "heb ‘086 '<
02 “Sth EEL

Go°Si9‘¢¢e
gl°2Si‘ tot

si*isc‘26e'9
22°01S*06S‘t
HG°6SO‘C1L ‘A

Lorvic* ligt

+9°10S°19
o£ *162 ‘639
¢2°Lio‘git

GG "926 ‘ens
9h ° 688 'SS9

28 °09f‘ff9"t
16*L6¢‘133
IG*Ese*cortt

19 °t0S*66E*1
ti lse*het ‘2
HL 96S ‘nbe'2

6S °n6E ‘609 ‘t
gz *096 'G6h‘¢
99 °6trh ‘208 ‘1

On 19H HLL
68 °2£5'°SS9
00 °h2S‘98

on"9eL*£9S
ig°ces ‘el
06°620°SLa*t

G6°9 ls “Oh
LS HS *t

000 *sh2 *6E
000 ‘236 ‘69

19°3f2*ote‘6ot

Witltn] G3137aN00

WHILIN] o3iL070v 1809 wioL *30vV1S

39V3T IW

oly IWwey3034 GQ3ivwiisy 39va IW BOVLNZOU3d

G3* lo *S6E
gua e ase
22 °s6£ *foe‘e
lo*tel*39l

ene
13°6£9'1S6
92° 10S ‘069

is
8 . oJ 9
its
gc°f93‘606'1

go"nin* Gon" t
O0°On LESH

1S°¢

tirsle‘lg

00°S21*265‘9
€2°fes‘szo't
g2*stg'oll*t

11°698 ‘Ont
29°906*682*t
sf*tle'0G9't

Ene ici '2ls‘2
16 “thd '9£0'E
13°639‘G16*L

80° 10S *6rL*€
GL°SLL eg'h
26°1n9‘l6s‘2

We pees
een
BL°6GL*11S*¢

98 °02h‘6L0‘%t
€Grece *1eG*2
81°S62°6f9'1

CE*His HLS

EHS *HOL ‘it
oe cstehis't

Bees
£5°65S *659*1
29°H92 "SEH

g2°090‘<19't
en°661 ‘9l2%2
16 °S09 ‘S36 "th

26°see*let'h
Stool ‘nlot2
L601 HB

o3110o7 Ww

Oly qWwy3034 |

000 ‘968 ‘Sg
000'LhI ‘st!

9£°20e‘ tls

rah AV:
02°26 ‘Ef3*L
22°H96*Esl‘t

02 *LhS*S16‘2
GL°612*S16‘t
16°002‘30n't

13°309‘601't
Qf 6G ‘nse
62 °CEG*en't

CrsLigtsie*e
Le-9rG cite
2k "0S ‘926

11-362‘ 120'S
pepe all
sl°eze‘slr*

02°99S ‘nik *9
ona
Le°gec*2eSu't

00 "00% 'S2 tL
95°90 69h" |
61 °Los ‘gil

19°93 *6EE
0£°29S‘91S'1
25°C00'62e'¢

28° ISL 91G *h
1€°SSG* Ifo
tl *<£9 ‘O16

LielsS‘ts2ttt
6t°Lh9 ‘2906
l9°S92‘6et'l

03"Lt6‘tol
lorieS*ene'e
gH LS9* tnt h

th 09h 6Ch'2
S*09S*091'S
29°09 '21S‘¢

*90t‘92L'OL
GG°6S9 ‘Hace
£2°£63*t1S‘e

Re Cae Nee
gS°L¢a‘tgG‘¢
G2 *625 ‘ols

Go*egl eget
66°221 GSE *h
1G°f3h*Slr‘or
He°sgl'ecn‘2
9e°se6‘esl*2
fO"'llo‘zis‘t

41809 WoL
O31vWi183

“+ ***Q3LZIBNOONS) BONVIVG
***G3L3IIMHOD NOILONYLBNOD

£°9l
bd
B°L6S‘2
€°f63

6°L6t‘t
6°226'1
16Ee

G*fo2*t
L*zo8‘l
h°2s9't

€*nel‘2
0°e26‘2
0°608't
1°9G6°¢

G*1lote
€rlis

SN
$38

uyeo to
AOS
mr

35vVFT IW

NO! LONYLSNOD YOI AZA08ddY

2£64 *o€ 3NNP JO sv

NOILONYLSNOD GvOY DIV Twu3034 JO SNlVLS LNaYYuND

B8O0VOY 2ITENY 4O NV3uNg
BYNLINOI YOY 40 ANSWLYvd3g B3LVLE ASLING

NOILONYLSNOO ¥30NN

O31L31dN09

seers eeomiOL

vere eet IWMVH
tees ON TWOAM

**NIBNOOBIM
*VINIDYITA 18934

*MOLONIHSYM
soWINTOMTA
+o LNORUB A

"*** *33863NN3]

***wLONWG HiNos
*¥NITN08VD HiNog
***ONV78] B0OHY

++ "WINVATASNNZd
settee NoBaEQ
+5 8s = WHOHVING

stern eee eon
***WLONWG HLUON
*¥NITOUVD MLYON

eee OA MIN
OO1X3W M3N
AIBU3P M3N

*3UIHSAONYH M3N
++ *VOWA3N
sts *wHOWUS3N

++ *WNWLNOW
*tunosstW
Iddissiesin

*VLOS3NNIW
+) NW OIHOIW
*SLL3BNHOVSEYW

78 SONVIABY IK
steerer aNIWYK
shes WNW IE INOF

+888 * *AHOMLNIY
totes es BvENYY
shee reser oumoy

sees eeyNW ION]
****S1ONITT]
sees sonva|

ttt e evi puosg
ss" *voIuonlg
+++ *3uvMvI3Q

****LN01L03NNOD |
° * *0avNON09
stew ENBOS ITD

“SVEN UY
++ *WNOZ ley
+++ owrveY Ty

.* a.
; 7 .
4 4 os i
' 1 }
Rit

Ce ee a Pitan d

A yt Pde? eM aT ER
Perera s Ge wants etal
ae 7
FAA EN CGR HOU 1"
Y “hh hy se ICA
a)

aie) uy wee KN
; t e | Awe ene
. ss oS erUety etavetod wt ea he iy ry € %
OOO NTN SNE Aa ‘ Was
poly *. AAR res Te eA tre hs Y
py cee S ey, \ Pestire areas ‘* ey % See » fy eee ee
\ Roa . ey inant Pues AN qt det Saat at iM KY
iY ee ‘ ‘ vel4 he WAC’ :
| COO Ct bl ce MAT hy

\ Sys A eh
i my ORs a : v4
Ona vay: 4 Ae tee mite) Sy ARI! a tt PSTN | he
Lea tee. # 8b. 4.

SAE DHT ey
ay) Bay

SoS
Pel? weet

: HUES QO
BONA HG Re TOR he # \
} te eC ATA ra AE an ” Ao Lite Lege ee We A
Wie dseeninie cu ie LAnioneseebecy 44 4 weet DIONNE OR, Kin
Oy acict tee ai bi Le LPI a a aad OG Alay un nate Nae hite BUA ith eR Setatone eC tS ‘
‘ +y5 Miata RK RAR HCD AV AP CR EE EB EOE SOM RLICIAC NLDA ACC A SU De OL ar he
Osh ah ene ate shige: ieee tea aR beet f sth ait iene wees
a “ Ph tate poh On Py ay STOMP ATS MONA RAAT IC NAL EE ebay
: . ) wh HEEL TAK: eR
enntee at BP Gte Rid satel rare a itary te aay an neteecsatectce Age ih ATER eh Aa
sreeata ney yeh uss CoN Wht! a? Daal Tb ATC GY CCR ee ay
J 4 ee u © is hee 4). ‘ ;| f ot
eu'ete! Pa nn) SUGPOVERLCUEU ERC LEE LEUER CE BC bee
A Aen he PRANAB ARS OLN ST Pt tae ia OR PO
a “er + Vy hs At SEA OCA Uh Ga Be OR RO Oh ke €
Sze eit SONA he AR A eRe bey 4
Vee hee Ley ey Y VRUAA HO AA COR Cady Con ih Ob Mb EEE
BUSCA Ne » CHAAR HFM OG 4 UA OAL
Wala ATA i} 4 ee tices WAY CANS
HEA EOE L AA Fle fo OO OA TOM ae an ty ore
, ‘ cs ith dyn tila deye se AN
oleae i Vee e 2s eh 4 Wiethte te athy
ies RK HLTA Mh heed & ae tet ¥ ie yas a
aa titan siya aie a As CL VUC ROLE TE kha e et ey) etal ; Ce eA t CERES ekg
Wain ke 4 GE POD te ty tet 6.03 Bi WR hb bei hce 4

vires 6 Taina Ady i
re ook Peeler Waa ya hz te pe hoi te OT PLT De Wt
bike WAR VALUES ons HELM Ee we uo bake aya WN he ba:

v W

pe 1
regi ANAND
Hite bit wie ake
4 CY Mc Reh Ot bona ba
aw ROA RE LE oA

vp este i either meth haya oho
ee RM): Ora

erste’ ciety
+4 $ wh

Reve ueaaanelet

ease Pe
Sere cd hiya ampere neta
« ay tres wiry
a tet yd yy ye We

Ophir ve

Cots Wh Oe

SOYA NEDA Ak ta a
qlee At &

CAG (oh F Peak wey 4 tebe i”

zi Darateascuteniete is 44, teh fo thaw Ww byte ‘ elect! LC ath Ais Oh ee DRL

St eh ik h DOCH AO Me Me Oh GAA Sete lect We alee
t

Be Lee: %
ee ROE
WN bE
Teskoey A8 4)
hs

(Hd Oey, WAL A oe, vhy beat te i Pe MATS Pe arte RR Ji teh Aa
SASSY wnat Chit WR CO) be beING an oe Cee OCA ania
4 le hig 4 ‘ 4 7 y
cM REN ran PO a WA aa i ee ee tik act

wn . 9 Le.
iF Pay UR Yeh Be teh twee §

bien f SHLAA We RMCG CER ACLIC MT oh unt WOR WENIER bh OE SY ,
Dy BRACE LON SAAC 4 ve teint) vat elites ue vitieiek et wo VAN ibd Cite a
panel) a Way t A Pay CVE heya hehe Mier ROD vet A RETA ADN ea ei As
th vay aA et p shoe Ct $2 Ohh OA od ae eR a Pea he Oe RO OR rn 6
atebattiyt 4 lad Sac EMU UA TAT ee CURA AER ERECT SAC Cee EG | HANG

Hi) “y PAS Myrhoy EMU OH AAA Db OOH tit CES VINO | how ett bokeh

ve at CO i Yc NODA Ac OO Oe PPR MAO Leeeee

\

BY \.
xa ‘ Water DUO NSHUN Fe Ot SCI TA
veka tay
t
be

VAG OV fh

Vb kes 4
PACT th ee bth ae &
:

in
i)
Na

tet) 4 H
+ 4 + Hy bee Pe FSG Wb FeO
i NI et ea TA 3 Le se yor bit Wi UOA UAE le bob
AKuny he ! Darente ’ Wane PROMEEC UST RIGA TA ett Ebr eee.
hart on i} Patiylaat (ace AU AAA DS Re LAM RNAS NAO BAA
VMs AND Lia halarcin ASMA, GA ea Tek TR A eTG Gre bce Leet Eee ee gre eh ae hi
awe aes CAN GUAT MAA DELS M LE CREM EOE ee Oth Oe bE WE 14) bhi ieee F
RIO eA Cot iain GA Hb APCOAAL Wr Ber b OY MALO or on re MRM LE RM ra tg 4
A ala de yeh rly! SiC sate eee thee PLO Stet SLSR Tare Matra wrk Arr Dray ch VL AOU
Nara Nate nia ares Whee ea ie COTS Bethe MRA es Cee eh Cay CERO LS UE Nee e bb by que
hie +h wk Be yn’ LARA PE WEE BUA EE POU De Sah SLR THR Mee bob eob 8 Ge Ppt kei Pi ay BO gk
Bae area Ta eee 2h PA MASLIN OO
sSrhih tee ‘ 4 aay EAC eB Ces : WCE IAA ek | Ok See be beak ©
syihn WEEMUA CH arc ctrauaee(AeC Ake ky Pa atte iar aati eke y neh AR ag ALL OL
Fi $ eb Uae: : yy eae teaver | Teta Eee NTA Gu Bret
Miter Ticatoubeeeanectsicltea eat (ouraeatescsdces GaaNy er teNaNCa oieheLy Cee peyartsunecg CUUSCHUN A RrECAnE aut th Ca ced
ae VANE E OVD TAR eee Ce ee ee RE LOVEE ECE LL hae
Wt SL Te MN re oot OC RG iT OO OO Ue pare Pai Pea Pe Wes ae a et Ts
APU ARON ASR LPG ML tA coh J Roe Nc eR LC VAY TNH LOE CO ee
hoa al atta Ke VACUO RRL Sau ki us ' ‘Sho , tah! cin bst ee
M ait fs oie Ty. eee Nh rier Siti Cas Ph reg yy WIN STAT gc Me BB A} MR Ah
HER AACR eee (NEV CCL Ae EO ee PES toe Ue KAPHA te Mh WAY Se
Dyer HRA RCE AGAR ELA ED re pe Aah HECEUE TAL ea eek bats
atirh yeas : i A Re MIRC se ; eee fr
esata) f { uti COE VAL CES ALE Weiyduth ubib byt bad

in ; Hy VHS GOH eds oa

. wate RRNA UE Et fi)
My att Se ¥ \ ( ih OLN RE ry Tine i cn St MEDC or ht
} nyse Neat, ALU SCE AMT aT We Aa oa SA ‘ PSS REM RATS oa m te
sey sn dyed) Hsia Ht ee v4 ath FAEeC RN ae Bh é "Ed EL UL eee eG
itarae mere apy i uD Pro RE DO ‘ SRM Wat ad BB eb
HRA A a i) aed CNT ST i Me i aA AY ' (: SHEP CEL ILE ERY S Tg
shsaseicd ote tas COORIOCED ar ae har Oris Oar eRe im ‘ VAR ECO TE Ce Bay
Sei reetsy ot RRA HORT oe OMEN Ob pe if vA AS OP Aaa 9 a Be GUC YC Oe
ee) sith MADERA RVG EV CU CEC Ob Eh y OO PRET EC LD Pada Wht We ow ha gto sat
SAN ck ‘ eh bates Cicer DU CAD ODOR OY CR IOAS LICR DUS
i "Ae AR ARO SAUL aiieisitetitel vite i, ai
agin 8,
£

HEEL UE UC MTEC EEE E
ray ‘ sas i ree Anta

Par er Meare ha ;

Avan) Ce y Ves
‘ WO 2 Ge VA,
hence at para

OM ae Oc hr
A NCD
Vagus earyete

‘ wi ai ULEre tah reached
: TC ie har ar AL Me in Fie cw he
ar Ra STM SE Yea Goh Mr a , A Wy y
uf , IO ry ih *y WE MEY | ra tita tiles " GrG bit Get ket welt ' rh
earn eit WET REE OEE EA AYE ARAL CE We Lit! CRS YTA CR nL a eA
AM APU PUGLICROCRC HW hs UM OFA oT AEA ANT Pe Mee ACH RO OTC A ae Re
siatescbat tcl stuerertues Car ttetatalna ate aplasia ta Aet tase GUM QuitetentcledeetL tN! oak
Neate = s SHEN MUTA UC Ree rN Cre CUR CG THE Ab (Ee feud

He OS g

GAN GEN HO ROUTE 0 5 COS MDAC Nore A Ot

Tho

i F 4 rt ‘
Veer vd tie MOLY be Rega MM babe B® Hub CERES ee be
* OA NEN ure Meat Feonrelbreatia inet ENED EO RM EY Ce h,
SADC ea RC MO PP PEW ER Cay
Dey eee Ob EY aT be baad ny
A ro Om CLO Pee OY ee A
PASS AG Oe Ma aA a ek HERA EO Eek (eA UCAS & ae
ATA MS BORN IM eS IC VEL VO UE CA CCH UA eee b
LOSE ent acer Py EN REO EO a eb Uk
Oe Dee bey eens ; Eevee a Let
b.) Vive ehh 4 I + tas
Cee 4 wy UM hy!
vit AS Uy SVE aes ar hits
Gerd nurs Pine NN { Viera.
tee ae :) Y
AAT BARA hy be 6 Not eae S ‘
A Opa a RM Glee had 43
Ae ee Ue G oe Ff, Kibet ae§ ,
WA CCE ta ta ee OC ce ata M
SED ERE LE EOD Ot A eat AAA D AS H
Coe Some Or te ee Neer oe Cee HRY EL tid
DET HA GH (be by tt bPR AVES LAE FN ee
DRAM AWE Ow Bot ih ee Gh dee ae: nro el ee ee
h PACED ES Le RE CE by tg fy A
1b 46 eh WALA ION DURGA KTR CITA ae
be } ) 5 bahia r ee bag
Ny AU OS VATE ath ROX Ce RI
ea ia a DAT ¢-4 i 4 HRN HAO,
f Thee Ae it ee v5 wi
FH OUR ' Wild GRE MESH LATIN EL ATL TES
POA eg Lary ree hiney Chiat POL. Vets .
ee ASR : ° ‘
Feet ey aU MEO OCIL WCAT BUMMER Ue DTC rh
Cee Rk Wy aha Ls la an EIU Mak de Sa
y rh See eae Wn ea ® P +
Way ah ea CM bey eh ie vey ‘ t
Ae Ah Fa EE ee nie be wet
Aa hao Th ae ee ee a «
NE AUC EN ea iatetas a a t
ULE DA ee 4,
A AIR Re 14 He tan * ue
Pee Oe} gs i ee We *
( HOM A Kova Pye a Oe Oat ed th ‘
i Valera tp CONS ORO OEM ORCL HVA E FEED eee hy
Ar Heh ee PNT areas hee ete Ne a mee ta ta a Oe he eye evs
* € 4 CER OHCe & Pe hh e cet t Phe et
: kin bee eee ah
Ay 4b rays se , DUA
Mtahati inti! aye VPA Vania eae yh yey Vieeey i wore ar he ke
ieee 254) 444 f aha aly ! FOOD ES ELE BEE RE
nied ta tan) ; PUAN ENP HED EEH Oe
a i sare h 4 Pha he eee ERM RS
Apap bya dana) Cee Ph ete Lewy bE
46 mete eat) i : RERYMMELOMME Rae
Gerla S +04) peated +4 thGees
COP AT a SE a UU at Tea AMAe TORE eae
CATE A as tek toate unc e vet beaer Le it eR i ya sere tlt Ahly ae \
TaPel creme Ay cPa Dae bole ok Pe ule Ye , sag + ey wy Se * ‘ uw ie
Ca eae ERE Are pre etay ene Mebane tte vals Dh ATU MOA HOUR WA AL ASU
F . Lae \.

4
bes se BOE 8 be
$ Mednecteetce ste Py’

ALP RM ry
yt arias Joti
A rarituretae attatett ace Y
i a ih eo Bu

hi Y PROVE EOL ERE LORS ty
Pah has ee ae wae yi GA yet bg t
+

ies Fh One OHS thon Wael

Sk AP ak eA id} See wee ey
tae Thee he wlth wale Ras uh Tay) Frese tauitet state tate aah
Rens CAEN ees LUMI Sr RM FREE idle IEA 4rd
he WEA RTD SION OGLE E HA Ue ee ara ies eae a4
vee $48 y e

wei he eee
Aa

*
£3

+4
re

‘\ ‘ ‘ * ii * ui .
bid tunnel ee aerue tans ae
Ba Ss Re

i Hie hs
WHA Sitter tates |
Lye eects dl
Mid

Sie hala
arachaanseants
3 vanaye ey ‘
baa et ieliudeianaeiees RE
; yah yre! eee Ly wa rhe eh bh 1G Oh sw

talat

i
Of
Mivea f

CHUMP REO Eee Le ae

es

+ thaskeg ri tanh r
’ hme are a eh tha: se WN:
sf NaN Bie i Y ‘
Pee en nat hi H Arana suave

3 ie Widatiainieatce cae Mires eY

eit b Fads ST edad By bead FUR ea wiey ta f
* yey ote * Pe eraT att At Nr ald dae,
ne Hara ae utuwoas sity! Use iether
re eee Cra eal ea tints aati deatecsittetcatd at
PLT aM bi foots Bins. ;

i vie Oa Heys x

ay!

Fees wee NC Ee

ee 4
CHOTA CE AE CELE ORE
+7 ‘ | ie! eee

TH MJ
RADA AOL &
yt stele ARM AD)
UUORNIU Cy he
Haier fie

HO

oe fy

Seve SAP SD
Shonen er wines
Che EH OHH HY

‘

ne ‘
ve en 1h oie arr!

ete Fl Ew HF ‘ Hobe
HARA Uy aA Av a iy

+8 8 a , IY
: eV Ve ote ee eee ee eg yaw ue .
\ Wieieeiee wes sone eh e rota eng ‘ ery?
RP eee SCAT ES MEN ane stet PAR CO t t PE CRMECKE EEL OS
fy AN sai Se seh ee ahd dA M) Ayes eh a) yy; ova 8 euaeLS
ees hee Yh Nihon errata “Puy amr Fun
te “G86

Se ee
ee. the